algicide, keep it all the time or when needed?

[pucklordofchoas]

I was wondering if you should keep a supply of algicide on hand constantly, or will your not need it if you can maintain decent chlorine levels constantly [/b]

[chem geek]

Though technically you can keep away algae if you maintain sufficient Free Chlorine (FC) relative to the Cyanuric Acid (CYA) level, some people find that difficult to do. So using a weekly maintenance dose of PolyQuat 60 algaecide prevents algae growth if the chlorine level drops too low. You can think of it as "insurance".

There may be situations of very high phosphates where higher chlorine levels would be required, but we haven't been able to sort that out yet. We do know that yellow/mustard algae requires higher levels of chlorine to keep away.

To prevent green algae, one needs to have an absolute minimum FC of 7.5% of the CYA level and the usual target is 11.5% of the CYA level. To prevent yellow/mustard algae in areas of frequent re-occurrence, a minimum FC of 15% of the CYA level is needed. Most (but not all) pools with saltwater chlorine generator (SWG) systems seem to be able to run with a lower FC that is about 4.5% of the CYA level -- partly due to the continual dosing but also due to very high and acidic chlorine levels in part of the SWG cell itself (so at least some of the water passing through gets exposed to that on each turnover).

Richard