I have a 20 gallon 30x12x18 inches. 20 watt flourescent lighting which I just recently changed from 8 to 12 hours per day. I add fertalizer. I have a gravel substrate. The tanks only been going for a few months now but I am getting brown leaves more so on the large plants than the smaller cuttings. Neutral Ph and no other testing equipment. Any ideas as to what's going on?