I have the same problem except its on the inside and only the top 1/4 of the tank because they guy I bought it from always kept the water low and I've tried everything and can't get it off I'll try the car wax but it doesn't sound fish friendly ???
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Yeah the cleaner should only be used if the tank is not housing any fish. I drained my 210 put all my fish in buckets and did the whole thing in one day. Washed the tank and wet dry vaccumed all the water out filled it up and threw the fish back in and Bob's your uncle.
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