Do my needle ferns pearl? Her's my answer
That is under only 0.9WPG T5HO. Low light according to the majority consensus
. However the CO2 is at 30ppm with 17.6x turnover circulation.
I wouldn't worry too much about pearling. It is a little overplayed in the hobby. Yes it means that the plants are producing oxygen but no pearling does not mean they are not producing oxygen.
Pearling occurs when the water is saturate with O and therefore cannot take any more into solution (sort of like diffusion) and it forms as bubbles instead.
If your water is not saturated then the O produced goes into solution and you don't see it. You can see this in most tanks where they start to pearl some way into the photoperiod. The O was going into solution for a while and then once saturated the pearling starts. Tanks with high surface turbulence may pearl earlier due to there being more O being brought in
A similar argument to people saying that one of the reasons reactors that dissolve all the CO2 are better than disc diffusers is that the bubbles rise to the surface and gas off. They don't question what happens with the CO2 in solution from the reactor. It still gasses off although they can't see the process happenning!!
So in summary pearling is a 'side effect' of photosynthesis. No pearling does not really mean the plants aren't photosynthesising. Just means they are not producing more O than the water is able to take.
On the photoperiod side of things I run both mine at 9 hours although the NPT Nano is full 9 hours where the Hi-tec 125Ltr is staggered to increase ½ hourly and has the full light for the central 4 hours.
They are both positioned to be out of all direct sunlight.
AC