Hello, I just received two marine bettas Saturday. They're doing great. Although they are showing signs of agression to each other. They really need lots of caves away from light. They really hate light. Which I knew going into them. I have lots of caves. However, one betta has shown dominance and claimed all the lower level caves for himself. The other has be ostrasized and is hanging out under my HOB power filter. Just enough room to shelter him from direct light.
They do sometimes swim in the open for me so far, surprisingly even with the light on. I have PC lighting though. I doubt they would under T5s or Halides.
I had a goby come with the bettas. The goby is gone, I presume one of the bettas ate him.
They are NOT safe with shrimp. Liveaquaria.com has good description of them. I ordered mine from somewhere else though. It says right in there not safe with shrimp.
I would guess within a day or two the cleaner shrimp would be gone and the Fire shrimp not long after that.
They are very Gorgeous fish though. Mine have this awesome blue outline with my lighting, and their main coloration is a brownish color with white dots and then his fake eye is a yellow color.
They're so neat. They shrink down at times and expend themselves. When they're fully expanded they're huge. They look very predatory when they fully expand. Very scary.
Mine have only been in my 55g tank going on 2 days now. In you're 170g I would think 2 would be very happy or 1. Whichever.
I might have to get rid of one if the agression continues, we'll see if they work things out. A friend of mine suggested poking the agressor with a stick every time it gets agressive.

(yes, it was jokingly.)