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Flow rate & current in planted tanks

Costa

Costa

Member
Joined
20 Oct 2016
Messages
354
Location
Athens, Greece
Gang, I have a 2m / 6.5ft, 900L / 235gal planted tank and I am really concerned re flow rate, nutrient distribution and sufficient current for my fish (around 60 small tetras).

The main tank is 650L and the sump 250L. Water circulation is carried out via a Jebao 5000L/hr pump that sits in the sump, and because of the height of the display tank I reckon the actual output is close to 3000L/hr. I am waiting on the delivery of a new 12,000L/hr pump.

So water is pumped from the sump into the main tank through a PVC tube that has a "T"-shaped head, located an inch or so from the surface of the main tank (60cm height), around the middle of the 2m tank. There is good surface agitation at the point where the water enters the main tank, but other than that there is close to zero plant movement around the tank, so the conclusion I draw is that the flow and current are inadequate.

Considering the fact that I have tetra fish in there that are considered peaceful (but then again are river fish, right?) I have the following questions for the good people of this forum to offer their advice on:

1- Flow rate will be improved with a much more powerful pump as well as the addition of a pvc tube for outflow with holes to act as a spraybar and run the length of the tank. The main tank is 60cm / 23in tall. Is this going to be enough?

2- I understand that flow rate and water current are two different things. Is that correct? If so, then how much current is acceptable for a planted tank with tetra fish? Apart from the spraybar along the surface, would you also add one or two wave makers?

I've only been in the hobby for 2 years so I very much appreciate all the feedback and suggestions. Thank you very much and have a wonderful day.
 
Well, considering there is no CO2 in the tank (except for a 4L DIY sugar-yeast solution I prepared and isn't doing much really) I can't complain. Plants are growing "ok" overall, but examining each plant one by one I see holes, melted stems, yellow tips etc. I dose with the standard EI plus some extra micro nutrients.
 
The issues you describe are more likely linked to insufficient Co2. If, in effect, you are currently running a non-Co2 injected tank, then low flow around the tank is not likely to be the culprit.

You seem in a half way house position - either drop the co2 you have, turn down the lights a bit and go low tech, or if you have demanding plants, take the plunge and get a full Co2 kit (and in which case you may also have to think about improving flow, but i'd do Co2 first, see if it has beneficial impact and if not look to improve the flow).

Really depends how much £££ you want to spend. That's my tuppence worth.
 
Costa said:
1- Flow rate will be improved with a much more powerful pump as well as the addition of a pvc tube for outflow with holes to act as a spraybar and run the length of the tank. The main tank is 60cm / 23in tall. Is this going to be enough?
Click to expand...
Hi costa,
As Edvert mentions, it's really difficult for us to visualize your plan just by looking at the words of your post alone. If you could draw us a couple of schematics ti would be easier for us to analyze.
I recall you had a thread a few weeks ago regarding the poor CO2 symptoms with your yeast based system. I don't thinkk you provided any details about the number of bottles or the sequence of the bottles. Yeast systems have gone out of fashion so there is not a lot of information around.

In any case, to answer this specific question, yes, flow rate always improves with stronger pumping. You will have to experiment with the length of the spraybar, the diameter of the pipe, as well as the size of the holes. If the tube is too long then the pressure drops as the water travels down the tube so that the holes at the far end do not produce as much flow as the holes closer to the pump outlet. The larger the diameter of the holes or the larger the diameter of the tube itself, the lower the current. The mass flow rate will be the same. So if you have concerns about the current, especially if you will have large finned fish such as angels or discus, this will help to make them more comfortable as they prefer quiet waters. For tetras high current is not a problem and they actually enjoys this. In any case, you will have to buy a lot of PVC and experiment. If you can get clear pvc it will be less ugly than the gray or black colored tubing.

Don't forget that you can also try simply placing the outlet of the pump at different locations just to see what kind of distribution you get. You always need to experiment to see what works in your particular tank.

If the main tank is 650L then this counts as a 650L tank as far as flow/distribution is concerned, not a 900L tank. The additional volume of the 250L sump does not enter this equation. It is relevant however, in terms of dosing, because sump volume definitely affects the concentration of nutrients. The same goes for medicine or any solute or reagent that you will add to the tank.

With that in mind, a 650L tank requires 6500LPH to satisfy the 10X rule. So you should easily be able to get good flow/distribution with a 12,000LPH rated pump. Honestly though, you should have been able to achieve good flow with the 5000LPH pump unless the sump is very far below the main tank or unless there is a long tubing run to the main from the sump.

In any case, with the new pump, as I mentioned, You should be able to achieve good distribution . Here is a 650L tank (no sump) using two of Eheim's largest filters at the time, each attached to their stock sections of 2 idiotic green spraybars. You can see the installation along the back wall. The total length of bars on each side was a little over 2 feet, with a gap in the center. So it can be achieved. Of course this was a pressurized gas system.

More importantly may be your execution of the yeast system, which we would need further details on to determine if any further optimization is possible. If you are sure you don't want to switch to gas then you need to examine that part of your system.
8395161534_fc0cd52e2d_b.jpg


Cheers,
 
Dear Clive, thank you for taking the time to reply!

ceg4048 said:
As Edvert mentions, it's really difficult for us to visualize your plan just by looking at the words of your post alone. If you could draw us a couple of schematics ti would be easier for us to analyze.
I recall you had a thread a few weeks ago regarding the poor CO2 symptoms with your yeast based system. I don't thinkk you provided any details about the number of bottles or the sequence of the bottles. Yeast systems have gone out of fashion so there is not a lot of information around.
Click to expand...

English is not my first language as I'm sure you have guessed; I will post pictures as soon as I return home.

Re CO2: Instead of the 1,5L Cola bottles I tried my luck with a bigger, 4 liter container for the yeast+sugar solution. Bubbles are coming out the airstone (I have placed it right where the water enters the main tank from the sump), but yes, I operate under the assumption that the tank runs without CO2... Like you said, yeast systems have gone out of fashion because they don't work consistently, even less so in a tank that size. Gas is going to be very expensive for this tank I'm afraid.

ceg4048 said:
Don't forget that you can also try simply placing the outlet of the pump at different locations just to see what kind of distribution you get. You always need to experiment to see what works in your particular tank.

...

With that in mind, a 650L tank requires 6500LPH to satisfy the 10X rule. So you should easily be able to get good flow/distribution with a 12,000LPH rated pump. Honestly though, you should have been able to achieve good flow with the 5000LPH pump unless the sump is very far below the main tank or unless there is a long tubing run to the main from the sump.
Click to expand...

Right, I tried to move the outlet around to see if I the flow improves, but sadly it hasn't. The distance between the sump to the top of the main tank is 170cm / 5.5ft, so the effective flow is pretty much halved.

I am planning on drilling the PVCs like in the picture you posted (my plants never looked so green and lush!).

Thank you again
Costa
 
Hi Costa,
Sorry, I didn't mean to say English was not good enough to explain. Even when native English speakers try to explain their ideas or their setup, we get confused. I have an image painted in my head of what I think you have (and so does Edvert) but the image that we each paint may not be real and we may give you advice based on the wrong image. For sure, your English is 1000X better than my Greek, so don't apologize. :)

I was thinking about your yeast issue, how to improve it's delivery, especially with the new pump. If the pump is in the sump, it might be better to send the gas into the sump instead of in the tank. If you do not have good movement in the tank the putting the airstone in the tank means that the gas will stay in one place and will not move around very well. If you allow the sump pump to push CO2 enriched water from the sump then at least the water tha does move as it enters the tank will send CO2 farther into the tank than if the airstone is in a stationary location.

Unless your sump is sealed at the top, you will be losing a LOT of CO2 as the water comes back down into the sump and splashes. Splashing causes the CO2 to escape, just like when you shake a coca-cola bottle. So if you are careful with the arrangement inside the sump and reduce the splashing as much as possible that will help to stop the gas escaping.

As I mentioned, the sump must be sealed as much as possible. The same comparison with the cola bottle. If you keep the cap on then the gas stays in solution. If the cap is off the gas escape. It's often very difficult to completely seal sumps because of all the tubes and wires but I mention it because it is a factor and it is even more important to conserve the gas with this type of delivery system.

Also, instead of one bottle, you could use several bottles and "stagger" them. What I mean by that is that you start each bottle on different days - one on Monday, the next on Tuesday. In this way, when the Monday bottle is declining, the Tuesday bottle still has strong delivery.

Also think about the type of yeast you can use. If you are using bread yeast, they are weak and they poison themselves with the alcohol they produce. If you use beer yeast they are more resistant to alcohol poisoning. Wine yeast has even stronger resistance. So they can continue to process the sugar long after the bread yeast have perished.

Anyway, these are some ideas - maybe not all are feasible but are still worth thinking about

Cheers,
 
Thank you again Clive for the comprehensive reply.

Posting some pictures.

First, the main tank and cabinet. It's 200 x 60 x 60 cm (net ~ 650L / 170 US gal). The cabinet houses the sump which is 250L / 65 US gal. The main tank is partly covered by a LED light unit and also some polycarbonate. The tank has been running like this for a full year, I haven't had any moisture issues (I check the wall behind the tanks regularly) so I'm guessing there isn't much evaportation.

20171022_111044.jpg


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A close up of the water outlet coming from the sump. It is "T"-shaped, as mentioned previously.

20171022_113555.jpg


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I've turned the outlet in such a way so that I get the best flow. Because of the PVC outlet T-shape, water hitting the back glass would create too much of a substrate disturbance, and so I think I found the optimal angle for the incoming water to hit the front and back of the aquarium to create flow (how good of a flow it is, is the subject of this discussion), without disturbing the substrate.

At the same time, the outflow also helps "crush" the CO2 bubbles against the back wall.

In the pics above and the video below you may see the sump inside the cabinet, the 4L yeast+sugar container.

20171022_111246.jpg


The sump is covered with a sheet of polycarbonate, mostly to avoid evaporation - so it's not sealed per se. Also there isn't much spalshing inside the tank. The only water disturbance is at the first compartment where water is coming down from the main tank and into the sump. The DIY CO2 container you may see at the back, I put it in two plastic bags to help with the temperature.

Also the video from the gas coming out of the silicone tubing and hitting the incoming water:



I thought about having the CO2 airstone in the sump. This is certainly doable. I will also look for beer or wine yeast, thank you for the suggestion.

Looking forward to your thoughts and feedback.

Have a great Sunday!
 
Hi Costa,
OK, thanks for the additional clarification.
Well, definitely, as I suspected that the way you are dissolving the gas is problematic.

First of all, it appears, from the size of the bubbles, that you are using an airstone, typically used with an air pump, instead of a proper ceramic CO2 diffuser stone.
Large bubbles have more buoyancy, and therefore they rise to the surface and escape more quickly. If you can get a CO2 ceramic disk it would produce much smaller bubbles and they would stay in the water longer, giving the CO2 a better chance of dissolving. If, in fact that is a CO2 ceramic disk then perhaps it is clogged with dirt or algae and if so, then you should clean it regularly with bleach. If you move it to the dark sump then you will reduce the amount of algae growing on the disk.

Absolutely I recommend you move the diffuser to the sump. Absolutely.

The cover on that sump looks pretty good. I don't think you need to do much more with that. The fact that the top of the tank is also covered is good for CO2 retention.

It's not clear from the video or photos, but it appears that the "T" outlet is in a corner? This is not a good place and it is also a really bad idea to have flow being sent to the back wall. No, no, no. Seal one end of the "T" or find a different kind of plumbing so that flow comes out only on one end - unless you plan to attach spraybars on each of the ends. If so, then yes, the "T" is a good thing.

Probably you have already thought about supplementing liquid carbon? I guess it's very expensive where you are but it would be great if you could afford it. It's very expensive with that tank size...

Cheers,
 
Hello Clive, thanks again for the advice

1. The T outlet is right in the middle of the tank.

2. I tried to use a ceramic diffuser but no bubbles would come out. I waited and waited but all I got was the yeast bottle to expand (it's hard plastic). I bathed the ceramic disk in mild chlorine and tried again but it was a no go. Has this happened to you before?

3. Can use Excel for sure, but is it going to make any difference?

I will put the airstone in the sump, thank you!
 
Costa said:
3. Can use Excel for sure, but is it going to make any difference?
Click to expand...
Hi Costa,
Yes, it will make a difference if you use it every day. Again, dose per bottle recommendation into the sump. Some people use double the dosage. VERY expensive for that size tank - remember, it has to be done daily. Also some plants do not like Excel. I see mostly swords, which love Excel. Liverworts, bladderworts and plants like Vallis cannot tolerate too much.

Costa said:
2. I tried to use a ceramic diffuser but no bubbles would come out. I waited and waited but all I got was the yeast bottle to expand (it's hard plastic). I bathed the ceramic disk in mild chlorine and tried again but it was a no go. Has this happened to you before?
Click to expand...
OK, that means there is not enough pressure from the yeast bottle so the pressure builds up in the bottle. If it was a stronger bottle material instead of plastic you might be able to build up enough pressure to force the gas out of the ceramic disk. The small holes in the ceramic disk have more resistance.

OK, when you mount the airstone in the sump, try to put the stone near the inlet of the pump to get the bubbles to be sucked into the pump - without allowing the pump to swallow the airstone! You may need to install a tube on the inlet side of the pump and you may need to install a mesh over the inlet to protect the pump.
In this photo I'm breaking the rule of protecting the pump with a mesh but in reality the airstone was sitting under the tube assembly so the weight of the assembly kept the stone securely in place.
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As I mentioned before, if you have the room, you may want to consider more bottles - but that means additional complications...

Cheers,
 
I did put the airstone right in front of the pump but the gas isn't getting sucked in. The pump's mesh is like 2" long, do you think it's too far away from the pump in?
 
I came across <these> a while back and also <this> sometimes diy'ing bottles are prone to leaks but both those items look like they would solve the problems of getting up to pressure. Takes two bottles so you could alternate the start times and getter a more stable production. Yeast tends to have a fast aerobic ferment then a slower more stable anaerobic one. the above are designed for chemical co2 production but can't see any reason why you couldn't use yeast in them to achieve the same thing.

What diffuser are you using? I find that the cheapen glass ones have no problem with diy it's mainly the atomisers that require a lot of pressure. As Clive mentioned wine yeast tends to do better than baking yeast, as the alcohol content rises eventually the yeast hits it tolerance threshold essentially getting sterilised by the alcohol, some specially designed sherry yeasts are available from home brew shop which have higher alcohol thresholds 14% and above but to be fair at this point the fermentation is so slow would probably be best tp change the bottle.
 
Thank you all for tour time. I hope I can return the favour.

Foxfish I thought about sticking the silicone tube into the mesh but then I won't be able to see if there's any gas being produced.
 
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