Originally Posted by SCMurphy
Increasing the heat does slow down the photosynthetic activities of some plants. Another possibility is an increase in bacterial activity adding both to your CO2 and the acidity of the water. You're fish will also respire at a higher rate with the water being warmer.
Ah...that makes sense too...obvious increase in bioload and biological activity switching from 20+ tiny harlequin rasboras to 5 pig-like discus and 9 just-as-hungry cories.