i cant seem to get my water in my 100 gal clear, i do water changes once a week, and i recently installed a timer for my lights as to no run them too long, the ph is a little low , 6.5 and nitrates/ites are low just above 0 and i dont have a problem with amonia, im currently running a filstar canistr filter plus an under gravel filter with 2 powerheads, because if the fish i have to keep limestones to keep the ph up, without it the ph drops, any ideas what im doing wrong or any way to clear up the water??