about heaters and internal filter

[awwer12]

hi~~ my name is Simon and i just registerd today...
i live in Canada and i am having some golden rams and
malawi chiclids...
so anyways, i haven't got heaters yet...

which one would you recommand for me to use??
there are too many heaters... Petcetera's, Big al's, Tetra whisper's, etc...

i had bought a Ehiem 2206 inter filter aquaball...
but the cruent of water is too strong that rams can't swim very well...
what should i do?? i thought to buy a spray bar but anythings not fit in...

help me~~