# CO2 on 25L tank advice



## messy_da_legend (Feb 18, 2006)

Hi, 

I was just wondering what would be the best form of CO2 addition for my to-be-set-up 25L. Lighting is 24w, and using aquasoil and PMDD ferts. 

Would I be best sticking to Excel or would a pressurised setup be needed if I were to stay away from DIY? I am on a low student budget, so price needs to be consideded. If pressurised is preferrable, which would you reccommend?

Can you help?

Thanks, Tom


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## Laith (Sep 4, 2004)

For a 25l tank you can go with DIY CO2. It's cheap to do and while Excel is an effective source of carbon, it is not as effective as CO2 is.

The difficulty with DIY CO2 is to keep the CO2 levels in the aquarium consistent. Some people do this by using two mixes in two bottles and alternating the new mixes.

Pressurized is the best option but for your size tank you'll get good results with DIY until you can afford upgrading. Tanks above about 150l get problematic with DIY CO2 because it's difficult to get the levels you need and keep them there.

By the way, PMDD doesn't contain Phosphate, which your plants will also need!


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## messy_da_legend (Feb 18, 2006)

I've found with DIY that each one I do takes about 1-1.5 days to start up. I could use two, but when both are working well during hte 'crossover' period wouldn't the mg/l go up too high?

Doesn't mono potassium phosphate contain phosphates? http://www.aquaessentials.co.uk/index.php?main_page=index&cPath=145_146


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## Laith (Sep 4, 2004)

Yes, you'll still get variations... that's the main disadvantage of DIY CO2 and minimizing the variations can be frustrating. But on a tight budget and with a 25l tank, it's better than no CO2. With two bottles, you need to find out how long your normal mix will last and then time the new mixes so that the new mix comes in about halfway through the life of the older mix. You'll still get a spike but I doubt you hit too high a level of CO2. If you do notice fish gasping at the surface because of excess CO2, increase the surface agitation to help balance things...

The original concept of PMDD did not include PO4 in the mix as the idea at the time was that by limiting PO4 you limit algae (not the case). So the term "PMDD" indicates a mix of nutrients without any PO4.


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