# Advice on flow rate



## james15 (3 Jul 2022)

Having had some rather stunted and distorted plants in my established 240l tank since switching from artificial to live plants a few years ago, I'm looking to improve things and give the plants a better shot at life. The first improvement I've made is using CO2. This has so far only been running for a day so obviously too early to see results,  but I'm hopeful that my plants will soon be doing better.

But this has now got me thinking about flow rate, and and whether what I've got is sufficient and the CO2 and nutrients are being distributed effectively. So the current layout is as follows: the filter output is located in the back right corner (this cannot be moved as it is the Fluval Roma 240 with the pipes coming through the base). There are two nozzles, one is angled slightly downwards and towards the heater to allow good flow past the heater. I have positioned my CO2 diffuser below the heater so the bubbles catch the flow from this nozzle. The other nozzle is pointed towards the front of the tank. The drop checker is located so that the output from this nozzle flows past it, but not directly across it.

Until the introduction of CO2 I was running an airstone 24/7 at the opposite end of the tank, I now have this turned off when the CO2 is on. So I'm thinking there is now very little water movement at the end furthest from the filter. There is certainly little or no visible disturbance of the plants at this end, and I'm not sure if the CO2 bubbles are making it this far (I think they're just about reaching the tall plant in the back left corner - see photo). The nominal flow rate from the filter is approximately 4.5 times the nominal tank volume per hour. Should I be looking at increasing this? I'm thinking I should consider adding a circulation pump at the end furthest from the filter. Is this necessary? And if so what size pump should I be looking at? And where would be best to position it? Any advice appreciated.


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## jaypeecee (3 Jul 2022)

Hi @james15 

One of our members (@Wookii) has done a lot of experimentation with flow rate. He will be alerted on this reply and may be able to advise you.

JPC


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## Yugang (5 Jul 2022)

Let me jump in, as it is a bit silent so far.

Sure, a 4.5 flow rate is on the low side as it is usually a 10 times tank per hour turnover that is recommended.
Having said that, advice on flow rate is perhaps not the best we can give you in this stage. Better would be to help you set up the tank that you like to create.

*You may  first want to clarify what end result you want to achieve*. A high tech tank, CO2 injected with lots of plants? Or not too many plants, or less demanding, where low tech may be good enough, if not better? How about live stock?

IMHO a low tech tank may be the preferred option for many. The issue with CO2 injection is that when you start doing it, you beter do it right or you will end up battling algae and other trouble. For your not so small 240 l tank, it will be quite a challenge to achieve good CO2 with your small diffuser and low flow. But if you're happy with a low tech tank, you may not be far away from a stable and successfull setup.

If your aim is to go the high tech route, you need to set up a relatively powerfull CO2 system that is good enough for your 240 l tank. You likely also need more flow. It would be good to have more plants, to make it easier to create a healthy and balanced ecosystem. You need to be prepared to do regular maintenance and cleaning. Etcetera. If you don't do it right, you may regret that you started to inject CO2 in the first place and start a battle with algae and unhealthy plants.

Sorry for not really answering your question, and playing the ball back. Hope that others chime in as well.


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## erwin123 (5 Jul 2022)

A us$3.50 usb pump pushing about 100l/hr at the substrate level was probably one of the most cost effective improvements to flow for me.

I now have one of these pumps just above a CO2 diffuser, so it sucks up 99.9% of the fine bubbles and pushes them along the bottom of the tank.


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## Yugang (5 Jul 2022)

erwin123 said:


> A us$3.50 usb pump pushing about 100l/hr at the substrate level was probably one of the most cost effective improvements to flow for me.
> 
> I now have one of these pumps just above a CO2 diffuser, so it sucks up 99.9% of the fine bubbles and pushes them along the bottom of the tank.


How much is the total flow rate of your tank?
Could you manage the CO2 of a 240 l tank with just one small diffuser?


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## erwin123 (5 Jul 2022)

Yugang said:


> How much is the total flow rate of your tank?
> Could you manage the CO2 of a 240 l tank with just one small diffuser?


my tank is an algae farm, so not the best example.
Maybe better to share Dennis' setup. (this looks like a 90p but his 120p [243 litres] is similar)


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## james15 (5 Jul 2022)

Yugang said:


> Let me jump in, as it is a bit silent so far.
> 
> Sure, a 4.5 flow rate is on the low side as it is usually a 10 times tank per hour turnover that is recommended.
> Having said that, advice on flow rate is perhaps not the best we can give you in this stage. Better would be to help you set up the tank that you like to create.
> ...


I think ultimately I'd like to be looking at something with lots of plants, as these always look incredible. But equally I don't want to try to run before I can walk. I think it would be a good starting point to get the existing plants growing healthier and then take it from there.

You mentioned my diffuser being small (it's just the one supplied with the system) -  would I be better with a bigger one then? What would be best to go for? For what it's worth, this one seems to be so far coping with the tank size, though I'm still in the process of making adjustments at this stage. But already the drop checker is taking on a more greenish hue, and there's still plenty of capacity to increase the injection level.


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## Yugang (6 Jul 2022)

james15 said:


> I think ultimately I'd like to be looking at something with lots of plants, as these always look incredible. But equally I don't want to try to run before I can walk. I think it would be a good starting point to get the existing plants growing healthier and then take it from there.


Low tech tanks without CO2 injection can look incredible as well, but I interpret your posting as that you want to step by step setup a high tech tank with lots of plants.



james15 said:


> You mentioned my diffuser being small (it's just the one supplied with the system) - would I be better with a bigger one then?


For my 200 l tank, smaller than yours, I have been using inline diffusers but for the last years only reactor. Perhaps it is indeed possible to inject your 240 l tank with a relatively small in tank diffuser. For dialling in your CO2 please refer to @Zeus.  excellent tutorial Dialling in the CO2 injection Rate and CO2 Profiles. You want your drop checker to go lime green, and have your CO2 as stable as possible, so that will be the proof if your diffuser does the job (I would be surprised, but may be wrong).

For a good CO2 stability in your tank you need a decent surface agitation, this is also where flow comes in. The following link may be helpfull








						Surface agitation & gaseous exchange in CO2 injected tanks
					

Surface agitation in a planted aquarium - yes or not ? This page explores why having some surface agitation and turnover is actually useful in planted tanks and actually makes tuning CO2 to optimal levels more easy.




					www.2hraquarist.com
				



Now we're talking about flow, you want a good distribution of CO2 and nutrient throughout the tank. Slow movement of water anywhere in the tank, without spots where water is stagnant.



james15 said:


> I don't want to try to run before I can walk


As far as plants are concerned, a tank works better when you have a sufficient mass of easy growing plants.  Now that you have started to inject CO2, especially in this transition period, you need to make sure you keep plants healthy and algae minimal. Add more easy and fast growing plants to your tank, this would be my #1 priority.

Make sure you clean tank and filter well, and have regular water changes. Build up of organics, besides CO2 stability, is a major cause for algae in high tech tanks. Confirm if you do proper fertilisation. Commercial plant food works good enough to start with.

In summary, I would use your current tools to learn to setup your tank with CO2 injection and get it to work with more plants. Do expect some challenges during the transition, we all get some algae and learning experiences when first using CO2 in a tank. From there, troubleshoot and step by step decide where  to invest for further improvement. This may be more powerful CO2 injection (reactor) or pumps for flow:


james15 said:


> I'm thinking I should consider adding a circulation pump at the end furthest from the filter. Is this necessary? And if so what size pump should I be looking at? And where would be best to position it? Any advice appreciated.


Perhaps others can chime in on this, I have a Maxspect gyre that works well but is expensive. There are many cheap and effective flow pumps and wavemakers on the market.

PS I realise that you just asked for advice on flow, but believe that answering that question without context could risk to put you on the wrong track with your new CO2 setup. Some, if not all of the above may have been known to you, in that case sorry for making things unnecessarily complicated.


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## james15 (6 Jul 2022)

Yugang said:


> PS I realise that you just asked for advice on flow, but believe that answering that question without context could risk to put you on the wrong track with your new CO2 setup. Some, if not all of the above may have been known to you, in that case sorry for making things unnecessarily complicated.


That's OK, all advice welcome. My interpretation of the situation was that flow rate was the next thing I needed to address, which is why I asked about it. But you're drawing my attention to other things I need to consider which I hadn't thought of, so I appreciate that.

So far the diffuser seems to be coping, I've been checking the drop checker and making the smallest possible adjustment once a day, and now it has reached the point where it is unmistakeably green. Not just greenish, but actually green. So I think I will, for now, keep the injection rate as it is and see how things develop. I will of course continue to keep a close eye on the drop checker and behaviour of the fish and plants.

Maintenance wise, I already perform regular water changes and have done so for as long as I've had the tank, as well as cleaning the filter regularly. I could perhaps be a little more thorough with my cleaning of the tank itself but that's certainly something I can manage. I did have a major algae problem in the past, both when I had artificial plants and even after switching to live plants. I have found nerite snails to be a big help, they do a fantastic job of cleaning the algae from all surfaces while causing no damage to the plants or surroundings, as well as being quite fascinating to watch. I realise that this does not replace manual cleaning and I am prepared to give the snails some assistance should the need arise.

Fertiliser - yes, I am using commercially available aquarium fertiliser according to the manufacturer's instructions.

I will study the water flow in the tank a little more, but I am fairly certain at this point that there is a dead spot at the end furthest from the filter.

And I will look at getting more plants very soon! Thanks for the advice!


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## Yugang (7 Jul 2022)

One more point, as I hope that my remarks will indeed help you setting up a high tech tank rather than just help you to increase flow



james15 said:


> So far the diffuser seems to be coping, I've been checking the drop checker and making the smallest possible adjustment once a day, and now it has reached the point where it is unmistakeably green. Not just greenish, but actually green.


You have a low flow, so likely a low surface agitation and low CO2 outgassing. It will be easy to get a green drop checker, even at a low injection, but the issue is that your CO2 ppm will not stabilise and keep increasing during the day. A dropchecker will not show that really, and may be cheating you. So your question about flow is correct, but what I tried to illustrate is that the best approach will be to consider the entire system. Flow is  not an objective in itself, but serves many different purposes and cannot be isolated from your overall objective and the entire system.

So to make the long story short ... Yes increase flow, and especially surface agitation. With that you will likely discover that you need to work on your CO2 diffuser as well to get still to a lime green drop checker. In the mean time, please be very careful with your beautiful fish and go slowly with any CO2 change while observing their welbeing.


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## james15 (10 Jul 2022)

Thanks for your help. Having now had a chance to observe over a longer period, the CO2 level is indeed increasing during the day, but it is erring on the side of too little CO2. Until I am able to improve the setup, I will not increase the injection rate any further as I feel too little is better than too much, as this way the fish are less likely to be harmed. The fish are currently showing no ill effects. Once I have improved my injection setup, I will initially decrease the injection rate and if necessary gradually increase it again.

So the next stage will be to add more plants, improve flow and surface agitation, and improve my CO2 setup. I have been looking at reactors, but nearly all of them are designed to accept 12/16mm hose, whereas my filter has 16/22mm hose. I don't want to reduce the hose size as this would reduce my already inadequate flow rate as well as having a negative impact on filter performance. So I have some options which I would like to ask advice on.

Option 1 would be this. It does accept 16/22mm hose so would not reduce flow rate too much, however the only issue is from reading the description, it is not a true reactor. It does have impellers to mix the CO2 into the water flow like a reactor, but does not "trap" the CO2 like a reactor does. However it would likely be a better option than my existing small diffuser. What would be your opinion on this? Would it be a suitable option for my tank?

Option 2 would be a conventional reactor using 12/16mm hose, and run it from a separate pump. This would allow me to boost flow rate, but I'm not sure if I could set it up in such a way as to provide the extra surface agitation needed, which would probably be a job best done by a wavemaker pump, so then I would be needing two additional pumps. Additionally this option would require siting the reactor within the tank, as the setup is such that I cannot run additional pipework in and out of the tank without cutting a notch out of the lid, which I would like to avoid doing. I'm sure I could hide the reactor somehow, but still less clutter in the tank would be better.

Option 3 - is there a decent reactor out there which is designed for 16/22mm hose without using an adaptor? This would be the ideal option but it just doesn't seem to exist.


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## LMuhlen (11 Jul 2022)

You could also set up a bypass in your return hose. This way you can control how much flow is directed to the reactor, optimizing it, and minimizing impact on your filter.


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## james15 (13 Jul 2022)

LMuhlen said:


> You could also set up a bypass in your return hose. This way you can control how much flow is directed to the reactor, optimizing it, and minimizing impact on your filter.


That sounds like it could be a good option. How exactly would I do this? Google isn't helping much.

Now I know what I need to do to improve the setup as a whole, this brings us back to my original question. We've established that additional flow will be required alongside all the other improvements. So what size circulation pump would I need? Given that my filter turns over around 4 tank volumes per hour, would a pump at the opposite end of the tank turning over 6 tank volumes per hour, thus giving 10 times in total with the filter, be the way forward?


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## john dory (13 Jul 2022)

I'd be looking at a fluval fx4 for a tank like yours.


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## erwin123 (14 Jul 2022)

Surface agitation & gaseous exchange in CO2 injected tanks
					

Surface agitation in a planted aquarium - yes or not ? This page explores why having some surface agitation and turnover is actually useful in planted tanks and actually makes tuning CO2 to optimal levels more easy.




					www.2hraquarist.com
				




This diagram shows why we need strong flow for CO2 injected tanks. After the water comes out of the outlet, it has to travel all the way to the other end of the tank, hit the side, travel downward, and then travel along the substrate.

In case you think this is all theoretical, here's a real life example from Libba's most excellent journal. Notice where his glosso carpet is the thickest? (even if you have a yellow drop checker, it doesn't mean that CO2 is uniformly distributed across the whole tank)


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## Yugang (14 Jul 2022)

james15 said:


> Option 1 would be this. It does accept 16/22mm hose so would not reduce flow rate too much,


This one, and similar on the market IMO overcomplicate what's needed for a reactor by creating complex flow patters with 'mixers' and vortexes. And, as you say, the example that you refer to seems more an inline diffuser than reactor (although there are some cross overs between the two methods). A simple reactor without moving mechanical parts (vibration, wear, maintenance) would be my preference.



james15 said:


> Option 2 would be a conventional reactor using 12/16mm hose, and run it from a separate pump.


I like the idea of a separate pump, because it is more economical than a big canister filter and can be used to really boost your flow and optimise the flow pattern in your tank. However, one might argue that for your tank volume you would the prefer a 1 inch diameter rather than 12/16.



james15 said:


> Option 3 - is there a decent reactor out there which is designed for 16/22mm hose without using an adaptor?





john dory said:


> I'd be looking at a fluval fx4 for a tank like yours.



This is a setup that I used in my tank and worked extremely well. The FX4 has a 1 inch diameter, and the (modified) AquaMediq1000 in the bypass is fitted to a 16/22 diameter.




AquaMediq is not cheap, and I modified it to such extend that one may argue why I spent my money on that in the first place. I hope that others can refer you to a commercially available reactor, or perhaps DIY solution. A reactor should be nothing more than a water column with bubbles, most if not all the rest is arguably overcomplicated by smart vendors

A powerful canister filter or external circulation pump, in combination with a simple yet effective reactor will work well.
Indeed, many users would argue that for your tank size an in-line diffuser works as well -- and they are right.
In another thread        I compare diffusers and reactors on various aspects     , and from my experience reactors are overall a better choice than diffusers (vendors probably prefer diffusers) for larger tanks. The comparison table includes my personal hobby project in the third column, which I believe is even better than reactors, but I omitted that from my previous remarks as it is currently not yet a main stream solution and has not been tested by others than myself.


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## james15 (14 Jul 2022)

Yugang said:


> This one, and similar on the market IMO overcomplicate what's needed for a reactor by creating complex flow patters with 'mixers' and vortexes. And, as you say, the example that you refer to seems more an inline diffuser than reactor (although there are some cross overs between the two methods). A simple reactor without moving mechanical parts (vibration, wear, maintenance) would be my preference.
> 
> 
> I like the idea of a separate pump, because it is more economical than a big canister filter and can be used to really boost your flow and optimise the flow pattern in your tank. However, one might argue that for your tank volume you would the prefer a 1 inch diameter rather than 12/16.
> ...


I like the idea of the bypass, I'm just trying to understand what's going on there. What's to stop water getting forced down both tees, causing overall little or no flow through the reactor?

Upgrading to an FX4 wouldn't really be an option. As my tank is the Fluval Roma 240 with the pipes entering through the base of the tank, I'm limited to 16/22mm hose. Best I could do in terms of a filter upgrade would be a 407. At the moment I'm thinking if I set up a  bypass to run a reactor from my existing 306 filter, I can then add a wavemaker pump at the opposite end to boost flow and ensure optimum circulation.


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## Yugang (14 Jul 2022)

james15 said:


> I like the idea of the bypass, I'm just trying to understand what's going on there. What's to stop water getting forced down both tees


Notice the red coloured valve at the top. When fully in open position, nearly all water will follow the least resistance and will not enter the reactor. When fully closed (90 degrees between red part and tubing), all water is forced through the more narrow path via the reactor. 
Water in my system would enter from the top right in the picure and flow to the left. Usually I would operate the valve at about 30-45 degrees from its pictured position, so that a  small part of the flow will be forced through reactor and the rest goes relatively unubstructed through the horizontal 1 inch tubing and mixes with the CO2 enriched reactor water at the junction on the top left.

On chosing the best canister, pump or reactor, I hope that others can chime in with similar size tanks. 

@james15  you may also search on this forum, a lot of useful information has already been discussed in existing threads. Other than the general advice on setting up high tech (rather than just a flow challenge) and my experience with my FX4 and reactor, I believe I can't add that much more in this stage.


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## james15 (14 Jul 2022)

Thanks for all your help @Yugang . That's enough information for me to be going on with. I'll get some more plants in there at the weekend, and see about installing a reactor. For my setup, I think a bypass on the filter outflow is the way to go, with a wavemaker in the tank to improve circulation. My final question for now, when talking about the desired flow rate in the tank, does that mean the total amount of flow from all pumps?


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## Yugang (15 Jul 2022)

james15 said:


> For my setup, I think a bypass on the filter outflow is the way to go, with a wavemaker in the tank to improve circulation


This would be also my preferred approach. A reasonable filter flow (16/22 should be good enough), powering the reactor as well. Then an affordable wave maker / gyre for optimal circulation.



james15 said:


> My final question for now, when talking about the desired flow rate in the tank, does that mean the total amount of flow from all pumps?


Remember, the 10* tank volume per hour is just a rule of thumb. Many in the hobby have great tanks with lower flow than that (especially since the real flow rate with loaded canisters, inline diffusers etc) is most often significantly (50%?) below the rating as given by manufacturer. With a wave maker however it is very easy to get good flow, for low cost. The key is that flow is not the objective in itself, it is all about distribution/circulation and surface agitation as mentioned previously.



james15 said:


> I'll get some more plants in there at the weekend,


That sounds exciting, hope you can treat us with a  picture soon 
Good luck


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## erwin123 (15 Jul 2022)

Yugang said:


> The key is that flow is not the objective in itself, it is all about distribution/circulation and surface agitation as mentioned previously.


100% agree - no point having lot of water movement at the top but multiple 'dead spots' at the substrate level.  This is especially a problem for 'tall tanks' where all the water flow is from outlets at the top of the tank.

Checking your flow at substrate level is pretty easy if you have an in-tank diffusor (another advantage of an in tank diffusor ...) just place it at each corner of your tank at the substrate level and look at the CO2 bubbles, do they rise up more or less vertically and only start moving 'sideways' nearer the surface?  Or do the bubbles start moving 'sideways' near the substrate.

when you see the bubble movement, you may understand why I am such a big fan of mini usb pumps (100litres/hr only) at the substrate level....😅

Of course, if you have a huge amount of flow, the risk of 'dead spots' decreases substantially.


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## james15 (15 Jul 2022)

I'll have a look at flow in the tank over the weekend. I think there is at least one dead spot. Just deciding what size wavemaker to go for. Unfortunately the manufacturer's guidance for what tank size they're suitable for is based on reef tanks which need much more flow, so if I went by that it would be way too powerful and my fish wouldn't be happy. But I'm thinking about 1500lph, based on what I've read in other threads here and elsewhere. I'm hoping that won't be too powerful. Please correct me if I'm wrong.


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## james15 (17 Jul 2022)

Update time!!

I've doubled the number of plants in there, and I've also replaced the faded plastic ornaments with real rocks for a more natural look (and they'll last much longer too!). The one on the right is still plastic, but being white to begin with you can't really tell it's faded and it still looks pretty good.







Unfortunately I damaged the rhizome on the java fern while removing it from the pot. I'm hoping it will still survive since from what I've read they can  successfully propagate from nearly nothing. But I'm prepared to replace it if I need to. I'm planning to get a few more plants later, but didn't want to get too many to start with as I can always get more if I need to. I'd definitely like to get some glossostigma in there.

Despite not being perfected yet, the existing plants are showing some signs that they are benefiting from the CO2 - in particular the Amazon sword which has been largely sitting there not doing much, has started producing a new leaf every couple of days. I've ordered a reactor, some plumbing fittings, and a wavemaker, so I can get to work on improving CO2 injection and flow. I disturbed some detritus when removing the old ornaments, revealing that there is indeed a dead spot on the left as I suspected.


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## james15 (31 Jul 2022)

Time for another update! I've now got a reactor and a lot more circulation. I started with a small wavemaker (Fluval CP2), and attempted to construct a bypass to run the reactor from the filter. Unfortunately I found that even with the bypass, the flow from the filter dropped off quite a bit, and also my reactor leaks a little bit (it is only a cheap one). The leak isn't bad enough to negatively affect the performance of the reactor, but enough to make a puddle in the cabinet so I opted instead to mount the reactor inside the tank and power it from a separate small pump (NewaJet 1200). The end result is very effective in terms of flow, and although it's early days yet the reactor seems to work well. Although the wavemaker is theoretically powerful enough to achieve sufficient flow combined with the filter, at least in terms of numbers, it would have been difficult to eliminate all deadspots. Now with the addition of a separate pump for the reactor in addition to the wavemaker, there are definitively no deadspots anywhere.

The reactor, pump and wavemaker are all located at the end furthest from the filter, and the reactor has an outlet located at the top (water flows in at the top, down the reactor column, then up through a pipe in the centre of the reactor and back out), to which I have added an adjustable duckbill nozzle, allowing me to direct flow towards the front of the tank and slightly upwards to create some surface agitation. Meanwhile the wavemaker is located further down to create a gentle flow in the lower part of the tank, back across towards the filter. The reactor does gurgle a bit and the flow is surprisingly powerful, so I have opted to run the pump on the same timer as the CO2 solenoid so it doesn't run 24/7. This way the noise isn't constant (not that it's unbearable anyway) and the fish get a bit of a break from the currents (though I have been careful to make sure there are always some areas where the current is always very gentle as gouramis in particular don't like it too strong, and in general the fish seem quite happy with the setup now). Meanwhile I still have an airstone running when the CO2 is off so surface agitation is maintained.

Having changed the setup I've got to experiment with the injection rate again but so far things look promising. I'm happy with the way the setup is working, and the plants are definitely showing the benefits. One of the new plants I bought a few weeks ago has already doubled in size, and the smaller echinodorus towards the front has started producing runners, something I've never seen it do in the three years that I've had it. The large plant at the back on the left (I can't remember what it's called!), which has been there since day 1, I have pruned quite heavily as the growth it had wasn't particularly healthy. Now with the proper setup it should have a chance do put on some healthy growth.


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## james15 (4 Sep 2022)

Think it's about time for another update, things are going well! The plants have put on a huge amount of growth and are filling out nicely, and the echinodorus towards the front has now started flowering. The flowers however don't last long before getting eaten by my pearl gouramis! I've also planted a small glossostigma at the front, waiting to see how successful that will be. I have a suspicion my lighting may not be enough for it but decided to give it a go and see what happens.


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