Hi all, I'm Kev, from Scarborough in UK, I've been reading the newsgroup for a while now (lurking as it were) and have a question. Scenario - we have pond, well actually because we moved its a Aquosis Vat measuring around 3m round by 1m deep - nearly 100 gallons, with an Oase Biotec 10 filter. Koi has been my wife's hobby for a long while. Weekly we get rid of the debris in the foam sponges in the filter, and we always take off the thousands of small snails that live on it (and transfer them elsewhere). All has been well over two house moves, including the first on of 200 miles. We've got quite good at moving Koi and keeping the bacteria alive in the filters. Anyway, I digress, all well but in midsummer we went to the Koi show in Newark, and got some VirusSure to condition our water for when any of the daft fish bump themselves on anything - we have one that just loves to leap and occasionally he hurts himself doing it. I blame the flies for coming too close to the water <grin> In the past we have used Melafix to treat them - very very successfully it has to be said. So when we saw the new stuff which was reputed to be better naturally we said we would try it. However (apart from the problem that it takes ages for a tablet to dissolve), we noted that the snail numbers crashed when we started using it - their shells seem to go very brittle and thin. We've stopped using it now and haven't needed to treat / condition the water at all yet and the snail numbers are only now just beginning to recover - although some are still suffering from this thinness of shell problem. Anyone else seen this, is it a co-incidence? Any other ideas on it? Your opinions would be appreciated Regards Kev PS fish growing well and healthy, now all size 4 to 5 (one almost 6) up about two sizes from original house. Pond building very soon now we have the new house under control.