I am already having trouble with the HC. I have been dosing with flourish excel daily (~1 cap full, and have done 2 doses of flourish comp). I know initially the light fixture was probably too low for them but I fixed that during the first 48 hours and it seems as though during the 48 hours after upgrade the HC is turning light yellow and even brown in some spots. I know CO2 injection is recommended but I didn't think it was an absolute must. Can't think of anything else to do at this point any input is appreciated...thanks.