I want to add one fish to my 10g shrimp and craw tank in a few weeks. My substrate is black with blue pebbles. My plants are almost all green with some with blue accents and one solid blue. My wall(background) is purple. I was thinking of getting one black fish to accent the plants and (match) the substrate. Which one of these will: 1. Do better by itself. 2. Do better in 100% freshwater. 3. Do better in a 10g. 4. Will make the shrimp feel more safe. 5. Do better without a heater. 6. Do better in 7.5-8.5 PH. 7. Do better in ultra hard water. P.S. Could I get one of each?