Maybe four of each? You should come out somewhere around 6-8 all together I think for that sized tank (someone please correct me if I am wrong). How large are your land areas? It is so hard to tell from pics sometimes. The measure of the surface area of the land will help to tell you how many FBTs you can put in there. Whatever fish you get, make sure they can tolerate colder water. Most tropical species will get sick in the temp that the newts will need. (I think that FBNs need room temp water, I know the newt I have does, but it isn't a FBN.) You can house common guppies (the kind they sell for feeders) in cold water, I breed them in my newt tank. Fancy guppies don't do so well in the colder water though. Goldfish are cold water fish, but they can get fairly large. Also, I wouldn't put in anything too expensive, because it may get eaten. Another good thing to add to the tank will be trumpet snails (make sure they are trumpet snails and not regular snails, the regular ones will eat any plants you put in the water, the trumpet snails will not, they only eat tank waste, so they also help keep the tank clean), the newts will eat the small ones, so you will have a food source in the tank for them. Ghost shrimp are also a good addition. I also have a chinese algae eater in my newt tank, he keeps algae from growing too much, and is a great tank mate, he's also fun to watch. He like the newt just fine, but if any of the other fish try to go in his little cave, he chases them off, lol. A pleco (what is commonly reffered to as an algae eater, even though they need other food to be healthy), would not be a good addition, because they get pretty big.
__________________
|