Is there sunlight shining directly on the tank? Natural sunlight is not good for fish tank as it promote algae growth.
I place mine in a position where it gets low-in-the-sky sunlight late in afternoon for about 1-2hrs a day with just one betta in one tank
The java moss from below and duckweed + salvinia from above cleans the water real good .... just little patches of brown algae which is easy enouggh to sponge off .... might throw in a couple of red shrimps to get them to start grazing
One question... any recommendations on a pelco species or that STAYS small even as an adult ?