Remember the 20G I got used?Well,the previous owner had added extra silicone around the bottom,inside.I only noticed after I got it as it was full of gravel.I cleaned it all out & discovered the caulking.I emailed her and asked if the tank leaked.She said no,that she did the extra silicone caulking because she had alot of rock in it and was afraid of the weight.So I filled the tank,no leaks...good.Bought Splotchie.Well,he has not been right for a few days.All water tests are perfect,water changes regularly.I have had a nagging feeling about the caulk.I suspect it was NOT aquarium silicone.It is hazy,most clear aquarium silicone dries clear.I researched and found that some caulking is TOXIC!!Yikes!I took Splotchie out & put him in the 25 with Lily & Silver.Overstocked now,but he seems better already,and I will add the filter from the 20 to the 25,so filtration will be approx.600gph.So now I have a useless tank.I think I will make it into a terrarium.

You could reseal the tank yourself, it isnt too hard. Have a look around at a few websites. I've resealed a couple of tanks, its nice and easy.

You might be able to remove it,
My dad always chalked this one part of the bathtub and it never stayed for long because of the water... I'd always pull it off.

Hmm, that is weird.

I bought a used tank and also didn't realize until I got home that there was some extra caulking. It's definetly not clear (though not white) but I haven't had any problems yet. *crosses fingers*

Much better to be safe than sorry, but are you sure there's no other factor that could have made your fish sick? What a shame to deny a goldfish his own tank

The caulking is hazy/whitish,and really globbed on(is that a word?lol)
And Splotchy has been out of that tank for 3 days and seems 100% better!
In the other tank he was acting crazy one minute zipping around,then floating nose up the next.I tested all params and Nitrite was 0,Ammonia 0,Nitrates 20,PH 7.6.Params were stable all the time because he was alone and 200gph filtration.