Agree on the Dwarf Gourami, I was given a couple and they happened to be males and they fought for sure and that was in a 72G tank!
Rainbow shark gets to 6 inches and can get really cranky at other bottom fish. I adopted one recently, so beautiful and he's been in my 4 feet long, 80G for several months.
Night before last, I watched him charging at every fish in what I assume he decided was his territory. For an hour non stop, eventually he went to other areas and seemed to stop bullying the other fish. In my case, there are a number of other bottom dwellers, so I plan to try him in my other 4' tank which has Kuhlis and Cories, in hopes he can settle in.
I kept an old 6.5 inch Red tail shark Also given to me. That girl would swim /patrol a figure 8 in the bottom 1/4-1/3 all around that tank scaring away any fish in the path. They all knew to just swim the other way and there were mainly Cories and some BN plecos. Somewhat peaceably. With 2 Siamese Algae Eaters which the SAE were from also adopted from the same home as the RTS.
To me, I feel that this particular fish needs a large area 4' - seems a minimum based upon my observations and your tank size might need to be upgraded for this fish if it gets to possessive of the space in the future. My RTS was boss of the bottom of the tank!!! I loved my RTS (RIP at around 7 years old - I had her for 2ish) and this new one has the bonus of the red fins too and is also becoming a favorite as well.
Also I made sure there were good hiding spaces to possess as territory, and open space all around the perimeter of the tank and there were 2 levels between plants DW and stones it could patrol the figure 8 type idea paths so it had lots of cruising areas.
As for white sand, it is beautiful but really hard to keep clean looking. A lighter color natural sand blend is easier to live with, especially with darker colors underneath getting mixed up into the white, my 2 cents
