Too little O2 = need more light?
3 goldfish - 7" common, 5" comet, 3" fantail
0 ppm ammonia
0 ppm nitrite
20 ppm nitrate
300 ppm GH
Marineland C220 canister filter
Coralife T5 48" - 108 Watts total
plants - hydra, giant hydra, java fern
substrate - mostly gravel, laterite on tank set up 5 yrs ago, some sand
water additives - NovAqua, liquid vitamin mix, florish excel occasionally
recent medications - treated for flukes with PraziPro last week, involves removing carbon from filter
I recently (a week ago) switched to a canister filter because I wanted to try to maximize the growth of my plants by decreasing the turbulence on the surface. I had previously (months ago) had two T5 light fixtures on my tank, but the plants under this condition grew with very tiny leaves - I think there was too much light for the amount of CO2. Under the current conditions, the leaves grow to normal size.
Up until a couple days ago, the fish seemed fine with the lower aeration in the tank - slow breathing, no gasping. However in the last couple days, their breathing has increased. I noticed this morning that their gills were very dark and they were breathing a lot more heavily. I turned on an airstone, and the situation improved within 15 min. It appears as though the plants and the fish depleted all of the O2 in the night, and photosynthesis wasn't kicking in fast enough when the lights turned on to replenish.
My question is this: if I add more light to the tank (ie the other T5 fixture), will the plants photosynthesize better and put more O2 into the tank? I am assuming that the goldfish are creating plenty of CO2 for the plants and I won't need to dope any in, but goldfish also like lots of oxygen. I would like to find a balance between the fish and the plants. I was thinking that because the partial pressure of O2 is so high, if I can get the plants to saturate with O2, then the fish will be fine. I am also open to running the airstone at night for a few hours to prevent the total depletion of the oxygen if the plants and fish together deplete it too quickly.
What do you guys think? Is light my limiting reagent?