'Probably good. I have 5 for a 55g. Good for eating scraps, not good for algae. Mix 'n match. They are one of the fastest snails (oximoron) that I've ever seen though.
All the best.
~wings~
I have one that came in as a hitch-hiker...I think a general rule of thumb is 1-2snails per gallon depending on size of the snails...Now this isnt a written rule just maybe a general guideline...you could probably add another 5-10 in the 38gal...you might also want to invest in turbos for sure...thats where serious clean up crew comes into play....