Had two crabs and don't think they did a thing.

I'm another with luck with manual removal. Some around the tank doesn't bother me but every once and a while, I'll break loose all I can reach with a dental pick and net it out (just hold the net in front of the return) and let the rest go down to the filter sock. Probably been about 3 months since did it last and need to get right up to the tank to spot any.

Why not try a Sailfin? Lots of people have a Q-Tank of 33 gallons or less. If it's a small one, go for it and return it/trade it/sell it once it's done it's thing.

A word of adive on the blow torch thing... Do it outside. It stinks. :)