Hi group

We have a 20 000 gallon water tank (with pump and sand filter) we use at or company for product testing. We don't use chlorine to control algae because it would increase corrosion of the stainless steel walls. Normally we use Hydrogen Peroxide, but that requires gallons and gallons to keep the levels up. Unfortunately we have been neglectful, and got ourselves a nice little algae colony.

On the advice of a local pool shop, we purchased a gallon of 60% polyquat, and dumped half of it into the tank. Two days later and the tank is far murkier than it was before! I can't tell if the colour is from an exploding algae colony, or the polyquat itself, but when I backwash the filter, the water stream has a definate blue hue, which matches the colour of the polyquat.

Has anyone else had this coloring problem using a "shock" dose of polyquat? Does it go away? What can I do to clear things up?

Brendan