dougall & OrionGirl >> Firstly thanks for the suggestion. Secondly there are no other livestock in there. Livestock will be in only by next week.I second the manual removal option. Keeping the feeding light--at this point, are there any other animals in there? If not, then manually removing them as you see them and crushing eggs should wipe them out pretty quickly. They only reproduce when there is a BUNCH of food available. That said, I happen to like snails and don't mind them in reasonable levels.
Prefilters are the easy answer to that, and they have the added benefit of being more surface area for biological filtration. I have, and will always have, them on all of my HOBs. Mine are a bit more DIY, because I don't buy a dedicated prefilter most of the time. I take an AC20 sponge, cut an X in it deep enough for the intake to fit in, and slide it up. Added benefit? I can buy a new filter for a new tank, take that sponge and either use it inside the media basket or as the prefilter, and have some biological filtration instantly.The downside is they can jamb up the works in filter impellers. More so a problem with HOB style filters.