Cloudy Tank

Hi,
I was wondering if you could help me? I have a 135g tank which I have had over a year with no problems. Until October of this year. I have a wet-dry filter systems with a built in overflow box. In the filter system I run about 3 Chemi-pure carbon filter bags and some phos-guard. I had 20 twenty african-cichlids. One day out of the blue the water turned extremely cloudy and all but 3 fish died. I haven't a clue as to what happen. When I tested the water all levels where within limits. I immediately did a 50% water change it reduced the cloudiness a little but not much. After a day I called the local fish store they came out and they did not have a clue either (wasted money) and did another water change Appro. (50%). After a week it was still cloudy so they advised me to do 100% water change, so I let the store keep fish did a 100% water change and let it setup for 2 weeks and the cloudiness went away. But when the fish returned after about a day the water turned cloudy again an has been cloudy ever since. Also I use cichlid lake salt and stress coat or prime when doing the water changes and I change carbon every 6 months. I also have done water changes every month (10-15%) since I have had the tank. The cloudiness, a milky white color.
Please Help if you can
Thanks
ldavis76

ammonia is 0 and nitrate 5ppm and nitrite is 0 and ph 8.4
all fish are dead except for three they all died the same day and i removed them all the same day and as far as the filter when doing a water change once a month I Rinse the sponge and change the floss filter pad in the drip pan and change the phos-guard.

liv2padl said:

within limits really doesn't describe your water quality ... what were the actual numbers for ammonia, nitite and nitrate? water changes every month of 10-15% are probably not adequate for a tank of African cichlids, though you're not overstocked.

are all fish accounted for? no deaths? a white milky appearance is 'usually' a bacterial bloom which might result from a dead fish or insufficient biofilter. have you cleaned your filter recently or at all within the last few months? what is your standard filter maintainance?

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