How to Fix a Cloudy Baquacil Pool
So your pool that you treat with Baquacil, Revacil, or some equivalent Biguanide santizer suddenly gets cloudy. Here's my solution, which works every time for me. Note that I have a 35K gallon in-ground pool. Adjust the amounts if yours is bigger/smaller.
Backwash the filter and recharge the DE (that is, dump some more DE in the filter return). This isn't the problem, but it won't hurt.
Dump 3 gallons of shock into the filter return, one after another without breaks. This will kill all the organic material hiding in your pipes. Expect to see lots of bubbles and ugly crap come out of the returns.
Get the Baquacil level up to a solid 50ppm. In my experience, low BQ level will keep the shock from clearing the pool.
Dump 4 gallons of shock into the pool. This will clear the cloudiness, whereas step 2 was to keep the cloudiness from coming right back.
Dump 1-2 BOXES of Borax into the filter return. This will drive your Ph through the roof, which kills so-called "Pink Algae" (which is pink, but is not algae). This is a preventative, to ensure the problem doesn't come right back when the shock wears off.
Wait 2 days.
Backwash the filter. It probably needs it, because all that cloudiness was organisms which are now dead and plugging up your filter.