I've run tanks of all sizes from 40 gals to 240 gals with calcium reactors and with just 2 part dosing. I've run all those systems with Kalkwasser simultaneously and without it. Finding the right mix of methods that satisfies the demands of the individual tank can be the difference between wonderful color, good growth and stability or the lack of all of those.
Anyone who tells you only need a CR for large tanks hasn't run one on a small tank, where they can do wonders.
I used the
original Knop C from 1995 to about 2000 and while it was a little touchy it worked great on a 50 gal reef tank.
Aquamax has made a couple of
Nano reactors over the last couple of years and I've read several threads with guys who run them on 60 gal cubes.
Aquamax products are just re-branded
JNS Aquaria's products made in Taiwan. They just came out with an update to their CRs in January so there may be a newer Nano CR coming soon.