I hate to be the bearer of bad news but goldfish need cooler temperatures than the Shark, Gouramis and Platies. They also need at least a 20G tank for the first and an additional 10G for each additional goldfish.
The Hillstreams also need cooler temps than the tropicals but they need lots of current and highly oxygenated water.
All are beautiful fish but not suited to being in the same tank.
Carol
I love these little fish! I have one in my tank, he is great though I would like to get more.
I would like to warn you to test ammonia, pinkish red underparts means that there is ammonia in the tank and these little guys are very sensitive to ammonia, nitrite, nitrate reading over 20 and low O2 levels, Just to let you know.
I love hillstream loaches, but I confuse them with the gastromyzons (butterfly loach). Apparently, it's OK to keep one of them (sorry, dont' know which anymore) in tropical temperatures but they can withstand colder temps. Not much help here, am I?
I do know that goldfish definitely are cold water fish, though, and that they need tons of space or they will poop the place down..
I love hillstream loaches, but I confuse them with the gastromyzons (butterfly loach). Apparently, it's OK to keep one of them (sorry, dont' know which anymore) in tropical temperatures but they can withstand colder temps. Not much help here, am I?
gastromyzons are hillstream loaches also as noted in the link I gave and you can keep one. But from experience they are happier in groups and display more of their natural actions in groups. Since they need a highly oxygenated environment higher tropical temperatures don't lend themselves to good benefit for Hillstreams. They will literally sufficate if the water isn't onygenated enough.
Carol
Do you know, you can tell me this another million times, I will FOREVER confuse gastromyzon, hillstream and butterfly and which are which. I know one is a synonym for the other and the other one is totally different and I will forever stay confused for some dark, unknown reason. Any info on these fish just doesn't stick in my brain!
LOL Armadillo- they are know by many names(butterfly loach, butterfly plec, borneo plec or loach) and the names are so confusing because of the variety of things they are called. Hillstream s like a huge heading all these 32 or so fall into. It's really hard to spell their names for one(you did very well with gastromyzons ) So it was easier to name them for where they came from, hillstreams. There is a really cool picture at teh bottom f that link that shows what type pf stream they come from.
carol
Hillstream is the cover all title, butterfly etc are common names, gastromyzon is the scientific name for one of the 32 or so different kinds Your getting there Never the less they are fascinating little fish and had had mine for about three years but unfortunately lost them during the recent move.
Carol
Another one: so hillstream is cover all for that shaped fish, grouping these very similar species together, then butterfly is the common name for gastromyzon, or are they two different species?
No problem, I love talking about this particular fish
We will kind of go in a circle here so bear with me The environment more than shape has caused them to be lumped under one cover all name of Hillstreams. They come from cool, fast running, rocky streams(thus hillstreams). Their shape( so evolutionary shape adaptation ?) allows them to graze on those rocks without being swept away.
All the different types have been sold under the butterfly common name so you really don't know whether you are getting Gastromyzon or Beaufortia or some other type. We finally ID'd mine as Beaufortia .
Carol
Do tell me if you get sick of this, but this is really fascinating, so I'll keep asking. If you get sick of it, stop me there, I'll understand. I'd read the odd article about hillstreams, and got myself totally confused. Now I at least get the classification (or what passes as one as this group seems a mess, hey?). So hillstream is the group of fish showing that anatomical feature. And people label a whole bunch of different species within that group butterfly loaches, including Beaufortia and Gastromyzon. Do I get it right?
Now the new question: what is the difference between Beaufortia and Gastromyzon, and do you know off-hand other species referred to as butterfly loach?
Sorry but you can't make me sick of this subject all the different species that are shaped like the Beaufortia and Gastromyzon are labeled butterfly something or other because of their butterfly shape. There is no one species called Butterfly Loach.
The difference between Beaufortia and Gastromyzon are basically their markings.these are pics of my Beaufortia
Carol
Similar Aquarium Fish Forum Threads 
Have you seen this article ? It's really good.
The environment more than shape has caused them to be lumped under one cover all name of Hillstreams. They come from cool, fast running, rocky streams(thus hillstreams). Their shape( so evolutionary shape adaptation ?) allows them to graze on those rocks without being swept away.