Light brown deposits after shocking?

About every two weeks , I add a bag of Cal-hypo to shock my 8600 g 18' ABG, mostly because I have several bags left over from the pool store. Normally, just use bleach to chlorinate. I premix the cal-hypo well in a bucket of water before adding, and continue mixing the settled portion until its all mixed well. Of course, the water clouds up for a day. However, always on the following day, I have several little deposits of light brown residue all over the pool, that I vacuum up. If this is cal-hypo, why is now brown , instead of white? Could it be something else, like algae, even though I've had no signs of algae before ?

thanks

Bob P
pool newby
8600g, 18', Pacifica, 26" High rite sand filter, 2.5 hp two speed pump