Black moors are categorized as "fancy" goldfish. These variants are the one of the biggest fancy goldfish rivaling the orandas, fantails, ranchus, ryukins and lionhead as they can gain a potential size of 12 inches if well cared for although 8-10 inches seems the normal size bracket. The general guideline for stocking fancy goldfish is start with 15g per fish although for a 55g, I would aim for at least 3-4 black moors.
Unfortunately, as I answered in the other thread, black is a very unstable color. The color will eventually change due to changing environmental conditions, foods and even genetics. This is melanophore migration. The lack of ultraviolet rays does not allow the fish to retain its melanophores which are in turn replaced by a pigment of another color particularly orange and yellow. This happens mostly due to lack of exposure to indirect sunlight and certain foods that help keep the black color steady such as green water. In Asia, black goldfish are sometimes raised in green watered ponds with indirect sunlight further retaining their black color which is desirable to many Asians. A lot of colors change from time to time. As far as I can see, only white and orange seem to keep themselves steady unlike other colors.
Their staple diet should be varied diet. They cannot thrive very well on flakes alone. In my experience, I don't feed them flakes. Flakes have very little nutritional value compared to pellets and gel foods. Aside from that, flakes tend to expand quickly and since these are also floating foods, they may make your goldfish much more prone to buoyancy issue. With pellets, I make sure what I give them are sinking types and should not contain mostly starch-based products which contribute to buoyancy issues by producing air as the bacteria digest the starch.
Considering commercial foods have a very low fiber content at 2%, additional plant cuttings and vegetable matter should be offered to allow them to flush out the excess foods from their digestive system. They need the high fiber to reduce the incidence rate of bloat or constipation. My goldfish relish several plants although some plants can still be kept without problems.
I use Hikari Lionhead, shrimp pellets and Mazuri gel foods as their diet. The Hikari Lionhead has 46% protein content so it is quite appropriate for young goldfish as they needed the protein for body development. Mazuri has about 56% protein content although fiber remains very low at 2% so I still add some supplements such as multivitamins and then plants with high fiber to their diet. Since some of my goldfish are raised in my ponds, they eat almost anything they can find including non-toxic tadpoles by treefrogs, young guppies, mosquito larva, bloodworms, etc.
My tanks are barebottom with plants kept in containers. I don't like to use gravel with goldfish as goldfish poop heavily and gravel just traps the wastes very easily. Go with either sand or barebottom setup but that's really up to you. As for the background, white is too glaring in my opinion. I just stick to black background with daylight tubes and they work very well in bringing out my goldfish's colors.
