Ok, first off, I know you are not trying to yell or any of those things, I respect and need constructive criticism, but I will also tell you where I am coming from and why. Now that that is cleared let me explain where I am coming from and why I believe the certain things I do.
If the goldfish stayed in a nonheated tank, with just the two of them, for the year or so that they did, and it was a 29g, without growing anymore than they have, then they cannot possibly be stunted, they just aren't getting bigger. 29g is plenty for two goldfish to have gotten bigger than 6". Granted, if they had stayed and kept growing then, yes, the 29g would have stunted them from getting to 9" and 12" but since they stopped this early I do not think it is a stunt, I think that is just how big they will grow. Also, the fancy, if that is what he is, controls the comet, if that is what he is, because the fancy has been around for around a year more than the comet so when the comet came around the fancy was already the boss of his lone aquarium.
When I got the puffer the store I got it from had him in with a few tropicals and the only judgements they had were that he wouldn't have enough room to hide at times, but since he has plenty plants and such, he would be fine they said. I have read that they do not require brackish water, it is just where they came from in nature. Also he hasn't been fin-nippin yet because he is only around 5/8" right now.
You also have to realize that these fish have just been moved into this 40g within the last week. Before there were just the goldies and sharks in 29g. They may grow now that they do have a little mroe room, but as stated above I do not see them growing.
Also, I am a person that sees expansion as a good thing. IF any of them do get larger and need the extra space I am there and willing to provide, this is just a time based thing. Since the room is available right now, I want to get the full sight out of it. In the future the goldies will probably have their own tank, while the tropicals would use one and the RBPs another.
I have also read that with the RBPs that a 30g is plenty for a shoal of 4-5 until they reach around 4" each. If anyone could confirm that it would be of great help because I plan on having a 65g and I figure it would last until they hit around 6" each.
Please keep the replies coming, I am loving them.
Until next time,
Erik Cooper