Protective F-8's? Twitching F-8?

[zboe]

My two F-8's have been doing great in my tank I haven't seen any fighting but some odd (to me) behavior form the F-8's the Hex tetra and swordtail. I've found that the hex tetra, swordtail and puffers are all sleeping together in either a corner or the big pot ornament I have (just a normal plant pot we took a hammer too and made a little entrance into ) and are all sort of hanging out together and in the past two days havent been far from each other. I almost think the Hex tetra and swordtail feel safe with the puffers as the tiger barbs leave them alone. The puffers do swim away from each other regularly The swordtail and Hex tend to stay with Vlad (the bigger of the two)
The I have three tiger barbs and they get aggressive at feeding time so I have lots of floating plants. Both the Hex and the swordtail have been bullied by the barbs in the past not so much as Ive thought that I will wake up and find my tank empty of all but the barbs or fish that are half eaten but enough that I decided I would have no more live bearers or small fish until the barbs die. Well the swordtail is the last live-bearer I have and the Hex is the smallest fish I have left. The Hex went missing for about two weeks and I thought he had been eaten by the barbs in the night and the swordtail had his little sword nipped off. The swordtail took to staying in the pot for a lot of the day, until I got the puffers. Both the Hex reappeared and the swordtail started being active again.
Im wondering does anyone else have F-8's that seem to protect smaller fish in their tank? I was expecting them to be nippy towards those two but instead they are more aggressive towards the barbs (which Im fine with the puffers cant catch them to do any damage and the littler fish are being left alone)
I just find it odd and cute to see those four fish just hanging out and swimming around together.
(EDIT0 I forgot to add that if the barbs come "too close'' in the puffers opinion they get chased to the other side of the tank
Also My littler F-8 Amenti seems to have a whole body twitch. Im not sure if its just how hes moving but it doesnt look like it he will just be swimming and his tail with curl in for a second and he sort of jerks to a side, it doesnt seem to affect him much but it is rather scary to see a fish twitch like that. I was wondering if anyone else has that problem with their puffer or knows how to fix it?

[RTR]

Please tell us what size the tank is and how many fish are in it, plus the water parameters.

[sevenyearnight]

Swordtails are fine in harder/brackish water that the F8 require, (SG of 1.003 - 1.005) but the other fish are soft/acidic water fish. Besides that, the very fact that the barbs are bullying the other fish is enough to rehome them, either in another tank, or to another home altogether. They are schooling fish and really need to be kept in schools of 5 or more. I'm not familiar with a hex tetra, but all tetras that I know of also need to be kept in schools.

RTR asks your tank size; Figure 8 puffers need to be kept in no less than 15 gallons per puffer, and this isn't taking tankmates into consideration, but since the only compatible tankmate you have as far as water type goes (not considering that he may be dinner one night) is the swordtail, a 30 gallon tank with only the 2 puffers and the swordtail is doable, but of course bigger is always better.

As for your questions, it is not common, but odd, what would appear to be friendships, do sometimes occur in different fish species. But again, the barbs are stressing the other fish out, and although they may not kill them with violence, the stress will shorten the other fishes' lives and make them susceptible to illness. Also, keeping the tetra and barbs in brackish water will shorten their lives and make them susceptible to illness, and there really is not compromise on the water SG and hardness, the Figure 8 puffers will not be long lived in freshwater, let alone soft/acidic freshwater; the water conditions are just too different.

The "twitching" sounds like external parasites/protozoan, but it could be a reaction to poor water quality as they are very sensitive.

[zboe]

Its a 35 gallon and I have been told its overstocked, Im getting a new tank for Christmas so Im going to be able to do something then but until then Im pretty much stuck with the barbs. All the schooling fish I have started in schools of 5 or 6 and dwindled down to this number and as until (tomorrow a petco is opening behind my house) the only petco's/petsmart's are about 30 minutes away and so adding more too their school was rather hard to do whenever one died. I have been out of test strips for about 3 weeks now but as a general the parameters are about perfect (cant find the last strip I used xP Im changing rooms right now) It is freshwater and Ive never added salt or anything to it in the life of the tank but I have used stuff like Cycle and other water conditioners and supplements in the past. I plan to set up a 30 gallon brackish for my Christmas tank or if I get the one I want off craigslist Ill have a barb tank and be able to move them into it.
It currently hs
3 Tiger Barbs
3 Black skirt tetras
2 F-8 puffers
1 golden dojo eel/worm/loach thing (acts and my pleco and entertains my puffers <3)
1 Swordtail
1 Hex tetra
The are no external parasites that I can see on Amenti so tomorrow ill test the water find out if everything is okay in the tank

[Pufferpunk]

What town do you live in? Near a big city? Can't you bring the other fish to a LFS?

[zboe]

Im on the edge of Denver Co.
From when I used to breed live bearers and my tank got over populated with fry a few years ago I understand Petco and Petsmart dont accept fish from people only their suppliers (at least thats what I was told)
There is a fish shop about 30 minutes away but my parents wont drive me or let me take a bus, so Im kind of stuck right now but might be able to talk them into it if I do alot of cleaning xP
Im off to the petco be back with parameters soon

[sevenyearnight]

Just an FYI, external parasites/protozoan are not always visible.