I found this on wiki answer:
WHITE MOLD CLEARED UP
I am going to assume you mean "water mold". Looks pretty yukky, shredded tissue etc.? Is that about right? I'm guessing you have or are now using a non chlorine sanitizer like Baquacil, or Soft Swim or other labels to describe a biguanide sanitizer. Here's the answer.
Get ready to reach deep into your pocket. The number of gallons you'll be treating is directly proportionate as to how deep you will have to dig into you pocket.
Search/Call the swimming pool stores in your area to see if they carry a product called: Assist (by Bio Guard), or Optimizer**& buy it. Assist is a tablet that is placed in the skimmer, Optimizer is granular and broadcasted over the water. You will also need a large supply of liquid muriatic acid. For every pound of Optimizer you will need to add acid. The proportions are listed on the Optimizer. Follow them.
The bad news is that not only is the mold you may have seen in your water, it is in all of your lines and equipment that the water flows through. It's a son of a ----- to kill. The good news is that it can be done.
DON'T CONSIDER DRAINING THE POOL(remember it's in everything the water touched) Chlorine doesn't kill it either (as you've probably found out). You will need to change the sand after you have eliminated the mould.
Once you have done that, Balance the pool water properly. Find a chlorine program that will work for you. There are some good ones. Get an automatic chlorinator, so all you'll have to do is shock the pool weekly, keep the pH in the PROPER RANGE etc. Find a good pool store to analyze your water and buy your products from them (if you want to get good advice when you need it) Use good products. Remember: Walmart, Lowes etc. don't test pool water and are "salesmen" they tell you only what the sales rep told them" They generally have no working knowledge of swimming pools and swimming pool water. I hope this helps. It won't be easy and it won't be fun, but it is do-able.
As a matter of information, BioGuard Soft Swim Assist is no longer available (since mid 2008). The above information is overall correct. One thing to keep in mind is that BioGuard Optimizer Plus WILL NOT kill or remove white water mold (WWM) or pink slime (this is NOT an algae - it is a form of bacteria). What Optimizer Plus will do is help to make the sanitizer - whatever one is being used - be more effective.
A better product that is showing good results both here in the US and in Europe is a product called AquaFinesse Pool Pucks. The Pool Pucks will remove the WWM from the surfaces they are affecting and growing on - which means virtually any pool surface, seen or unseen. Pool Pucks are compatible with any and all pool sanitizers and sanitizing systems and they will NOT affect pool water chemistry.
You may want to read up on bio-films in general. That is the root cause of WWM, Pink Slime, many scaling issues, etc. Here's a good link to bio-films.