Does anyone know the cheapest place online to buy Physan?

[Wild Orchid]

Originally Posted by DavidCampen

The active ingredients in Physan - benzylalkyl ammonium chlorides (also sometimes referred to as quaternary ammonium chlorides or simply "quats")
are used as a disinfectant in many other products. Swimming Pool and Spa supplies are a good place to look, it is used to control algae, you will need to go to Walmart or Canadian Tire and read labels.

Here are a couple of products:
Algaecide (5%), 4L | Canadian Tire

Liquid Algaecide 15%, 3.78L | Canadian Tire

Thanks for this info, David and Silken!
In fact, I've already bought a bottle for Algae-Kill 40% from the Wal-Mart.
Can you advise on dosage though? I'm concerned that this is a very strong, concentrated stuff and I'm not sure that even a drop or two per gallon could cause harm rather than help?

Thanks again!
Lilia