I'm new here and to planted tanks, so I'm kind of learning as I go. I did keep unplanted tanks for over 5 years previously however, although the place I lived when I had my previous tanks had very different water conditions than where I live now (much harder water previously). I'm trying to adapt to that while learning about plants and it's pretty daunting at first. I've got a new 20H tank that I'm trying to set up with some healthy plants. It currently has some lower light plants like Anubias and they're doing pretty well but I want to get it going with some new PC lighting that I have and DIY CO2.
I have 50/50 Fluorite/gravel mix for substrate, and 1 true SAE + 3 small honey gouramis. Algae is under control right now (SAE is doing a nice job of keeping it off the plants) but I don't want it to explode with the higher lighting. I'm giving it a small dose of Flourish weekly and changing 15% water every 3 days. It's been up for several months now and has fully cycled.
Now my problem....growth seems to have stopped in the last week or so, and I think the problem is lack of carbon (pH has been creeping up from the level in my tap water). I have quite low KH of ~2-2.5 and GH of 9, so I'm afraid that adding CO2 will cause my pH to drop very quickly. Should I raise KH before adding CO2 (with sodium bicarbonate)? If so, how much should I add? My pH is 7.1 out of the tap and it's risen a little bit above that now that the plants are established and growing.
Oh, forgot to add...it's getting a small dose of Excel every other day. It helps some (plants are growing), but not seemingly enough, which is part of why I want to go to the CO2. That, and to lower the pH some.