cloudy tank and fish loss

Question
Help! My tank is cloudy and I'm losing fish.  I have a 2o extra high tank with only 10 fish.  1 pleco,1 cori, 1 platti, 1 flying fox,and some tetras. I have an eclipse 1 system with a bio wheel. My gravel is about 2" deep. The tank is 6 months old and completed it's cycle months ago.  My water tests perfect except sometimes my PH dips to 6.8.  The temp is at 78. I feed my fish very little every other day at the most.  A tiny bit of flakes, 2 shrimp pellets and an occasional algae pellet. I used to do a small water change every week or so but my tank was cloudy and my local store told me to try doing changes every 3-4 weeks, still cloudy.  When I change the water I put in Cycle and Prime and a tiny bit of aquarium salt. I've tried acurel-F and an algae remover, nothing. I put in a poly filer bag, nothing. Not only is my tank constantly cloudy but starting back in the middle of August I've lost a total of 21 fish.  Most of the fish lost were balloon molly's, platty's,and cori's. According to my local store I'm doing everything right. This tank belongs to my 5 year old.  He names his fish and is crushed every time we lose one.  I'm at a complete loss. PLEASE HELP


Answer
Heather,
sounds like you have enough trouble with this tank,
frankly I would start the whole tank over at this point.
also, algae remover will compromise the bio-filter as it is copper based and the only way to get rid of it is dilute it.
by starting it over I mean, drain it to the gravel, after you have stirred it and cleaned it, you do not have to remove it from the tank, a gravel vac will work fine here.
have the new water on hand and ready , put nothing in the water.
watch feeding amounts and don;t add any fish untill the tank stablizes.
when doing water changes do not change all the filter media at the same time.
you may want to check the water at the tap for nitrates, ph, heavy metals...
I suggest this because everything else at this point has not worked, so we are at a place of desperate times call for desperate measures.
if this does not solve the trouble then a complete tear down, sterilize and reset is in order.
let me know the outcome.