Weaning off CO2


Junior Poster
May 15, 2010
Hello All,

I am new here and to planted aquariums (been reefing for around 14 years) and I have some question re: CO2. Four weeks ago i set up a 10 gallon tank. It is lit by a single 27w spiral CFL and recieves 4 or 5 hours of direct sunlight maybe 2 out of every 5 days (gotta love them San Francisco Summers!) For substrate I used hyponex potting soil covered with fine beach sand. I dose EI. I inject CO2 at a rate sufficient to turn a 5dkh solution solid green. No algae anywhere.

Anyways, long story made short: the tank is doing very well. Too well in fact. I don't want to have to prune every few days! I am thinking about removing the CO2 and lowering the amount that I dose and maybe even dropping to a 18w bulb.

I am guessing that just yanking off the CO2 would result in a disaster ... Over what timeframe do you'll think that it is safe to slowly reduce the CO2 levels?


Jun 14, 2010
San Diego, CA
Instead of reducing growth with CO2 or Nutrients, I'd keep them high, and limit growth with light.

Limiting any one nutrient is an invite for all sorts of different kinds of algae, and if you control growth by limiting CO2 you give Algae a distinct edge over the plants in your tank.

If it were me, I would keep everything the same,.. block the sunlight, then adjust the CO2 so it remains around 30PPM with the new light levels. I might also consider some slower growing plants to replace the ones that are most troublesome.

Hope this helps!

Left C

Lifetime Members
Sep 26, 2005
Burlington, NC
You could swap that 10g out for a 15g tall. It's 6" taller with the same footprint. Dose the nutrients and CO2 for a 15g tank and keep the same lighting like you have now.

The height lowers your PAR at the lower levels of the aquarium's depth plus the extra height lets the plants get taller.

Anyway, that's what I did when I cracked the glass in a 10g.

Tom Barr

Staff member
Jan 23, 2005
Try a simple 1x15w FL under counter type light.
This will be plenty of light.
Switch to Excel for a month or two.
Then taper off.

No water changes.

Dose the EI, but at 1/2 the normal dose, but only 2-3x a month.

Tom Barr