Removing ammonia from "baby" fish tank

I'm an intermediate skill fish keeper and am aware of cycling a tank and
such. I've got myself into a situation that I'm not sure the best way to
resolve.

In my 75 G. tank my two of my freshwater angelfish spawned. I removed the
eggs and have successfully raised the fish until now there bodies are about
the size of a 50 cent piece. I also have two subsequent spawnings at
various stages of development.

If this turns out to be worthwhile (if I can find a LFS to buy these from
me) then I may invest in larger tanks, but right now I have a 2 G.
"hatching" tank, a 5 G. intermediate tank, and a 10 G. "final" tank. It is
this 10 G. tank that is giving me problems.

The 10 G. tank is seriously overloaded. I'd guess that I have 50+ angelfish
in that tank. The ammonia is high, and I cannot get it down. I'm very
puzzled by that. I've even resorted to twice daily 50% water changes and
the ammonia is still too high. At this point I'm not sure what to do. If I
can find a LFS to take them, they're ready to go and the problem will be
solved. It may be another few days before I get there.

Should I:
Put ammo lock or something similar in the tank?
Continue with the big water changes and not worry about anything else?
Move the fish into 5 G. buckets with fresh water?
Something else....

If I can make any money off these guys, I'll invest in a larger "final"
tank, but I'm not there yet.

Tony