please help, problematic tank!

I agree with bracekeeper, take care of the water conditions first and then treat for the problem, preferably in a hospital tank.

A good rule of thumb is not to treat in main tank!
 
It seriously looks to me like the two medications mixed in the water has created this problem, beofre changing meds like that you should at least run carbonfor a few days to make sure the prior med is completely gone before adding new meds. This is why it is beneficial to use a hospital tank. you can just change all the water. I know this is not what you want to hear however if you want to save the fish, fix the water.
 
Also, I hope you plan on massively upgrading that tank to a MUCH larger size or have someone else's tank. Not the main issue, but the puffers are big waste producers and won't help matters out any.

I would use hyposalinity. Velvet looks very different than ich, also it's deadly very quickly so I'm going to say that I am leaning to it not being velvet or you woud have at least one dead fish, if not almost all of them with it left untreated. Treatment for ich, i would use copper as a last resort (and as noted, not on puffers) and hyposalinity first. Certainly water change(s) would help lower ammonia and help out. I would also increase circulation. I have a 29g and have a koralia 2 on it and it's not high flow, at all, IMO. Some meds deplete oxygen levels so it's better to be over that than under and airstones really don't do much in saltwater tanks.
 
You have way too many fish in a 30g, especially messy fish such as puffers. One valentini requires a 25g tank just for it (gets to 4 in. in size). The porcupine and the star/stripes get to 18 in. each (require 120-180g min tank size). Also puffers have a tendency to be aggressive to each other- sometimes across species. I am not familiar with keeping clowns or damsels- from what I heard they don't get as big as the porcupine (the larger puffers may eventually eat them-almost all puffers are aggressive to some extent-just because a article states that such a species is more docile, don't assume your fish will be-every puffer has a different personality). Damsels I heard can be aggressive- that can lead to more problems. The ich could easily be from the stress of so many non-compatible fish in such close quarters. Get a bigger or more tanks and separate some of the fish. For more info on puffers check
http://www.thepufferforum.com/forum/ug.php/v/PufferPedia/
 
You have way too many fish in a 30g, especially messy fish such as puffers. One valentini requires a 25g tank just for it (gets to 4 in. in size). The porcupine and the star/stripes get to 18 in. each (require 120-180g min tank size). Also puffers have a tendency to be aggressive to each other- sometimes across species. I am not familiar with keeping clowns or damsels- from what I heard they don't get as big as the porcupine (the larger puffers may eventually eat them-almost all puffers are aggressive to some extent-just because a article states that such a species is more docile, don't assume your fish will be-every puffer has a different personality). Damsels I heard can be aggressive- that can lead to more problems. The ich could easily be from the stress of so many non-compatible fish in such close quarters. Get a bigger or more tanks and separate some of the fish. For more info on puffers check
http://www.thepufferforum.com/forum/ug.php/v/PufferPedia/

Thank god someone else noticed this!!!! What made you think you could keep a porcupine and stars and stripes puffer in a tank that size???
 
Not to pour salt on an open wound, but the tank is only 6-8 weeks running. Even a more reasonalble stocking list should be added slowly, allowing your bio filtration to catch up. Thin out the stock, get those params to 0, and test as often as possible to get a better idea of the condition of your tank. Good luck, I hope things clear up soon. Keep at it!
 
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