Begin adding 6 gallon doses of PLAIN 6% sodium hypochlorite in the late evening; test your chlorine levels with OTO (yellow drops) the following AM. If you find that you do NOT have a STRONG yellow test result, repeat the dose that evening.

There are several reasons for a very high chlorine demand, but by far the most common (this year, at least) is high stabilizer levels in the fall bio-degraded bacterially to ammonia in the spring. The levels of ammonia can be VERY high, and can require enormous doses of chlorine to resolve.

You should also use borax to maintain the pH in the higher range (7.6 - 7.8) while you're cleaning up this mess: if it is ammonia, the intermediate products that form as you break down the ammonia are much less noxious at higher pH levels.

And. . . you should get a Taylor K-2006 test kit (see the test kit info page in my signature) so we can find out what's REALLY happening.