had this problem myself. Star Tron, as mentioned, available from West Marine did the trick. It eats the bugs up allowing them to pass instead of clogging the filters like regular biocide.

Problem two was I still had a clogged tank strainer. Could not get it to budge to clean it so I simply switched the return and feed lines under the hood. At first I wondered if the return line [now the feed] went all the way to the bottom of the tank and it seems to so thats not an issue. I'm sure this fix isn't as good as removing the tank and cleaning it but it's been 2 years and I haven't had any problems.

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Cheers,
Bill