I have read that Bioguard Backup is quite effective in taking out these bugs in addition to proper chlorination. I cannot find anyone local that sells it, but many sell other 40% - 60% algaecides. I have read that Bioguard Backup is 50%. In any case, does it have to be 50% or would the 40% algaecide do the job? Does it have to be Bioguard?