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CO2 & Light Demands

skeletonw00t

Member
Joined
16 Dec 2011
Messages
324
Hi,

I have a question about the CO2 concentration in tanks & the light demands that follow it.

Does the CO2 work in the same way that ferts do - in that the CO2 uptake is capped & that upping CO2 will just mean that the CO2 will not be a factor in limiting plant growth.

Or

Does CO2 work like lighting - in that increasing CO2 will increase the plants demand for light & nutrients.

The reason I ask is that i have very high CO2 in my tank & am also dosing EI. I am still getting slow growth though. The reason I suspect is that my lighting is low & my bulbs are too old.

I use 2 x 25watt T8 tubes in a 130 litre tank - the bulbs are around 14 months old.

I was considering upgrading to a T5 Luminare - or maybe just trying replacing the bulbs.
 
the T5 lights will give a better PAR rating, so in turn will put extra demand on the plants. This will increase growth rates as long as the C02 is good enough (which after following your thread, i'm sure it is), and the rest will follow. Incidentally i'm running the same lighting on my tan as you and i'm going to probably end up doing the same as you and getting a T5 unit for my next scape as i found it quite hard to grow HC under T8 lighting in my tank.

so, in a nutshell, having loads of C02 will not make the plants grow quicker, the lighting will do that, the C02 will be the building blocks.
 
skeletonw00t said:
Hi,

I have a question about the CO2 concentration in tanks & the light demands that follow it.

Does the CO2 work in the same way that ferts do - in that the CO2 uptake is capped & that upping CO2 will just mean that the CO2 will not be a factor in limiting plant growth.

Or

Does CO2 work like lighting - in that increasing CO2 will increase the plants demand for light & nutrients.

Co2 uptake is capped by light. Light drives demand for co2 - nutrients. Adding more co2 allows you to use stronger lighting, which will then drive up demand for nutrients. Excess co2 won't cause more demand for light. Light is the overall driving force.
 
I agree 100% with Spyder. Also, what do old bulbs have to do with anything? CO2 grows plants. If you are adding CO2 and your plants are not growing faster then they did when you did not have CO2 then you have to immediately suspect that your flow and distribution are poor. In any case you need a frame of reference because growth rates depend on species as well as light, CO2 and nutrients. Are you looking at slow growing plants like moss and carpet plants? They grow very slowly compared to stems. There are lots of people using T8 and who have great success and excellent growth rates and it is always a mistake to lose ones nerve and add more light, because you must confirm that your CO2 diffusion and execution is solid. If it is not then adding more light will simply trigger algal blooms. The choice is yours of course, but if you are even asking this question then I can tell immediately that the answer is to stay away from high light until you figured out how to grow plants with the lights you have.

Cheers,
 
CO2 & Light Demands

Hi Ceg,

Well my flow is around 20x - driven by my filter & a koralia.

Co2 is being injected directly into the filter at about 6-8 bubbles per second. The drop checker is always yellow too. Co2 does not have a solenoid.

I am dosing ferts - an all in one mix & am dosing heavily on that - the exact mix im using is what you recommended in the ei tutorial forum (for an all in one mix). Im overdosing on this pretty much so i know nutrients arent an issue either.

I'm not getting algae either - just slow growth.

So my only conclusion is that my light isn't strong enough to encourage faster growth in my tank. Afterall 50watts of T8 light in a 45cm deep 130litre tank is pretty low lighting really?!

I might try replacing the bulbs as this increases the Par rating according to Georges article in Pfk.

I remember about 7 months ago when i was getting better growth even when using a poorer co2 method (difuser in the corner of the tank) and i think that was because the bulbs werent as old & were therefore giving more light?
 
Most people don't have any problems with old bulbs, unless they don't turn on when you flip the switch.

The problem with 45cm has less to do with light traveling 45cm than CO2 traveling 45cm. Therefore I would question your distribution. If you're not getting algae and if the plants are not rotting then that's a good sign certainly. Are you certain that the only difference between now and 7 months ago is just the bulbs? Nothing else has changed, like big leaves that have grown up blocking flow?

Adding more light definitely increases growth rates, there's no doubt about that, you just need to ensure that you have ticked all the boxes and that more light is the last on the list of things to tick.

Cheers,
 
Well the things that have changed over the 7 months are:

CO2 & Distribution - i previously used a diffuser in the tank corner & this was pumping LESS CO2 into the tank... so if anything my co2 has increased & distribution improved due to the direct-into-filter method.

Plants have grown & may be blocking flow slightly... BUT I have compensated this by adding a koralia - 1500ltr/hr pump & i can see clearly from watching the tank that the flow is strong all around the tank.

The plants aren't rotting no & there is very little algae (I just clean the glass & rocks weekly) but the growth is slow & my Staurogyne growth has slowed in particular.

Honestly I'd love for you to be able to sort of assess the tank hands on as I reckon you'd be just as at a loss as me - It's like I am missing a key ingredient for successful growth .... only I'm not.

CO2 - always yellow - being driven around the tank by 20x turnover.
Nutrients overdosed so always available.
The only thing I could think of would be a light deficiency...

I currently have my lights on for 6 hours a day - do you think I should increase this and see if it helps?
 
Just a thought... Somtimes the in-line diffusers create a sort of bubble haze through the tank. Mike Appleby, who I consider a very credible commentator on the planted aquarium hobby, has intimated in one of his posts that some of these bubbles might collect in the CO2 drop checker and distort the reading. Perhaps this is worth considering given you are using an in-line diffuser, as it might be that your CO2 levels are not as high as you think. Good luck in any case.
 
Ok Ceg - as requested here are some pics

the rocks need a clean!

As you can see i have a problem with Dirt - it seems to collect all round the tank - even with 20x turn over.

Could it be that this is some form of algae and not dirt? I'm beginning to think the scape is just that old that it needs to be redone?

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DC is always this colour

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I was thinking as co2 bubbles rise it will show higher reading near the surface but 99% of you plant mass is in the lower water column. There could be a big difference in co2 levels.

I remember another thread about this tank a while ago and think the outcome was lack of ferts. If I remember correctly you changed ferts then had mega pearling and things were picking up. Your DC does look a bit on the yellowish side.

How is the flow returned to the tank? Which way is the flow running? A shot showing this would be interesting.
 
CO2 & Light Demands

Flow goes from top right towards left of the tank - then is pushed down the left side and along the bottom back towards the filter intake.
 
CO2 & Light Demands

Also i dont have any co2 bubbles in my tank as its injected into the filter - so no bubbles will rise into the DC
 
That's a very dirty tank so it needs to be cleaned more often. Dirt stifles plant growth and if that is organic detritus then it is pulling Oxygen from the water column. What is your water change schedule?

Yur mindset should be to keep the tank immaculately clean. Layers of dirt on the surface of the leaves blocks CO2 and nutrients from penetrating across the tissue membrane. When you do a water change you should use your fingers and rub the dirt/film from the leaves so that they are pristine. This is definitely part of your problem.

I cannot tell from those shots whether it is indeed diatomic algae or just regular detritus, but whatever it is, it's stopping plant growth. Do 99% water changes if you need , and as often as you need to get rid of that muck, and quick mate.

Cheers,
 
CO2 & Light Demands

I agree Ceg - my problem is that i seem to be making it worse by cleaning it... Im doing 2x weekly 50% changes & i was vacuuming the tank and everything. I just can't seem to shift all of the dirt - its so annoying!
 
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