Unfortunatly my tank has started leaking from the bottom corner. I have moved the fish into another tank as a temporary measure and emptied the leaking tank. I found a crack in the bottom pain of glass in the corner so have repaired it with evo stik "wet grab" sealant. I have filled the tank back up and have left it for 3 days now and it seems to be holding. However a friend suggested that putting my oscars back in the tank may be a bad idea as there may be chemicals in the sealant that are being released into the water? Has anybody had any previous experience with this kind of thing? Thanks

you will not have any problems if you use a non-toxic silicon sealant.
www.bigalsonline.com/BigAlsUS/ctl3684/cp...conesealant10ozblack

Most silicone sealants (like the stuff you use around your bath) have an anti fungicide in them. This is poisonous to fish. If you use this sort of sealant on a fish tank the anti fungicide leaches into the tank and will kill your fish. So check on your sealant to make sure is has no additives and is only pure silicone sealant. If you are unsure remove the sealant, You can buy silicone sealant remover, and refix your tank with sealant bought at a fish shop