From my limited experience with a White cap...
Hardy, EXTREMELY timid fish.
Does not fair well without a shrimp to pair with.
Will pair with tiger and randall's pistol.
Whitecap's will get lost in anything bigger then a 10-20g tank.
Purchased mine in Jan. with a candy cane pistol. Very tiny 3/4" each. They never found each other when introduced to the 75g and the goby would only come out of the rockwork at night. Broke down all the rockwork and put the whitecap back into the QT tank to pair up with the shrimp, the shrimp managed to hitchhike a ride into my 100g sump full of rock....... I do hear him snap from time to time
Already had a yasha goby in shipping at the time. The two goby's in the QT were extremely timid and hid all the time and we were having no luck finding a shrimp to pair them with. The goby's were not looking very good at all, so when a pistol shrimp became available we grabbed it right away and introduced it into the QT. Unfortunately it was a tiger pistol shrimp , which is not the symbiotic shrimp for either goby, so I was a little concerned. Within 2 minutes he paired up with the whitecap and they started to burrow, I did hold my breath watching to see if the tiger pistol was going to take out the expensive whitecap or accept it!
The yasha hid in a clam shell for two days by himself and was looking near death before I pulled the shell on him. He took off across the QT and into the burrow with the whitecap/tiger pistol pair. All three have been living happily together for 7 weeks now and became less timid. The yasha will stay out of the burrow until you got within a foot or two of the tank, the whitecap will keep his head out of the burrow until I open the lid.
Decided to set up a Fluval Edge nano in our home theater room for the trio and transferred them over 2 days ago. The whitecap went solo until we scared him out of the rockwork towards the yasha/shrimp. They are back to their timid ways now, but are starting to make regular appearances.
Once the two goby's mature more, currently only 1"(Whitecap) and 1.5"(Yasha), I may look at moving them into a larger tank. Since I want to be able to see this trio at work regularly, a nano was the best option.