hi all. i have had my set up for sevral years now, but a few months ago (6) i changed from gravel to sand and added plants a co2 system and also a new fluval 305.(not all at once i might add) all this was done over a 6 week period, now the plants aren't growing all that well and like the title says my sand is also turning brown (brown agle-diatoms) i have been doing 1/4 water changes weekly syphoning the sand whilest doing so, but it keeps coming back .. i have 11 tetras 10 other small fish, sry i cant remember there name 2 catfish and a plec in my 200 litre tank.. any and all advice will be much appreciated (i'll take a picture to add later(battery is dead in the camera) many thanks