Very Cloudy Water in Established Aquarium Please Help

[absoluteaquaria]

I do aquarium maintenance for a day care, while my typical expertise is in coral reef setups this day care tank is an assorted african cichlid tank.

Tank description:
75 gallon tank been up and running for about a year and a half
9 Assorted african cichlids and one Pleco
Ammonia = 0 Nitrite = 0 PH= 7.9 Nitrates = 30 Temp = 80

Out of nowhere the tank went cloudy about 3 weeks ago, since I have been doing very large water changes which reduce the cloudiness but only temporarily. Filtration was a HOB carbon filter as well as a canister filter (the canister filter has been removed to ensure the cloudiness wasn't coming from the filter media to no help)
It is possible that it is some sort of sudden algae bloom however we have never had one before and there is a very basic normal output light on there on about 10 hours a day which doesn’t seem like enough to make the water severely cloudy, the cloudy color is somewhat green though.

The only possible idea I have left is the sand substrate (which was there before I got there but I know is not aquarium grade substrate and I’m not sure where it came from). However the substrate has been in there the entire life of the tank and has caused no problems before. Is it possible the substrate could just now be excreting something to cause cloudiness even though it was causing no problems before and if not does anyone have any idea what else it could be.

Thanks in advance.

 

[Rivercats]

Put some of the water in a white cup and see if it has a green tint to it. If so the tank has a green water algae bloom. You can do a total 3 day black out followed by a large WC and only run lighting 6 hours afterwards. This method often works. Or my preferred method is to run a UV sterilizer on the tank. Many on this site has had very good results with this product... Green Killing Machine Internal UV Sterilizer with Power Head at PETCO. It will quickly kill all the free floating algae. It is unsightly but you only need to use it 24-48 hours after the water is clear.

If the water in the cup doesn't have a green tint then something is causing a bacterial bloom. These blooms usually go away on their own in a matter of days but can last much longer. A UV sterilizer can also be used for these blooms but you need to find the root of the cause and correct it. Check nitrate and phosphate levels. Also has the bio-media in the filter been cleaned with tap water?

 

[hennaartist]

^ agree, if it's not an algae bloom, you may just have to let the bacteria bloom run its course. Generally it will be about a week (without water changes, as that will just prolong it).