When you say "dwarfs" do you mean H. zosterae? If so, a 12 is way too big! For a 10 gallon tank you would need to pack at least 5 pairs of dwarfs in there, if not more. This is because you would need to load up the tank with BBS in order to get the concentration up high enough, but then you would need lots of ponies to eat it all so it doesn't fowl the water.

Most dwarf keepers suggest 2-3 pairs in a 5 gallon, or even a 2.5 gallon, to start with.

H. angustus are a smaller seahorse species that *might* be ok in a 12 gallon, provided it had ample foilage to hide in. Its a tough one, I would recommend at least a 15, but it probably could be done in a 12. Height is important too, how tall is the AP12?

-Diana