Saltwater Aquarium Fish for Marine Aquariums: Kaudern's Cardinal - Tank-Bred
I like the Benggai Cardinal and I do suggest 2 or 3, but no more. They can do fine on their own, but I think they look better when in a small group. I also think they prefer a small group, but a large group is when they get aggressive towards one another. They thrive in a group of two or three, but not in a bigger group.
If you are doing a Fish Only with Live Rock, you do not need to worry about calcium as that's for more of a reefer thing. The white could just be poop, or the rock just being cleaned. I wouldn't worry about it, as long as your test show good results, I wouldn't worry. Plus the salt we use has a good dose of calcium already that would be enough for a FOWLR
tank. If you can take a picture and post it, so we can see. It would help us a lot in determining if you have an issue.
Feed once a day and enough food where they can eat it all in two minutes. Remember your clean up crew needs to have a little food as well. So you should be fine. I feed my guys Frozen Brine shrimp, Krill, Mysis Shrimp, and Plankton. Squid as well! I got a pack that has a lot of food in it. I also feed Spectrum Pellets and a good marine flake food!
What I normally do is put my tank water in a small dixie cup and drop the food into it to thaw out. I put some pellets or flakes in to add to the mixture and I stir the food up and drop into the tank. I found a cube is normally enough for all my fish and I have 7 bigger fish right now. you might want to cut your food in half if you have smaller fish as to not use as much.
They do have different size pellets for smaller fish as well. So check that food out!
I would also suggest Garlic as an additive. It helps to get picky eaters to eat. It may also help improve the immune system, but I don't think that has totally proven!
Amazon.com: Kent Marine 00657 Garlic Xtreme, 1-Ounce Bottle: Pet Supplies