i have a 6 week old 125litre setup with about 1.5wpg of light and diy co2 (my drop checker with 4dkh water is consistenly green). am using james' pmdd. following a water change (changing between 25-50%) my plants (and unfortunately the algae too!) seems to pearl for the rest of the day in a way they don't at any other time. what is likely to be in the tap water that does this? is it - 1. not pearling at all but chlorine coming out of the water as gas bubbles, i add dechlorinator to the tank and then top it up with a hose. this seems unlikely as the most light exposed plants seem to pearl the most, with the lower leaves not doing so. 2. the tap water contains much higher co2 levels. this is hard to tell as the drop checker gets out of contact with the water and turns blue in contact with the air while the water change occurs, however once back in contact with the water it appears roughly the same green shade. 3. there is a nutrient in the tap water that i am under-dosing. as an experiment i doubled the dosing of everything, but could not reproduce the pearling, even transciently. (testing with my imperfect test kits suggests that nitrate ~25, phosphate high at 5.0 (up from previous levels because of doubling up fertiliser), iron 0.5-1.0, potassium not tested! but sure high too!!). i guess my money would have to be on number, co2, but wanted to reassure myself was not gassing the fish with loads of chlorine or alterantively missing something else? any thoughts?