I've got a 30 g tank, and its got a common (9-10 inch), oranda (3-4 inches), and 4 fantails (2 inches each).
Things are getting crowded and my fish are becoming less active. I need to upgrade but I dont have a whole lot of room and I live on the 3rd floor where Im afraid a ton of weight may not be a good thing. I'm thinking about going to either a 55 gallon or a 70 gallon.
I plan on eventually getting a Ryukin (if I can ever find one!) and I know I'll end up buying some more but not for a while, and I'll upgrade from there. I might be moving out to a bigger place next year, or later this year in which case I'll have more room for a bigger tank, but I really need to get my fish into a bigger place ASAP.

Any tips on buying a new, bigger tank? I have an AquaClear 30 gallon filter that works great, I was wondering if I could simply buy another 30 g filter and put both of them in a 55 g tank? Technically it'd be 60 g of filtration, right? Im trying to cut down on costs.

Welcome to Koko's Orandaa!

I'm sorry to hear that your fish are getting a big overcrowded and less active.

The first thing everyone here on koko's will say is that your tank is overstocked by a lot.
Your 30 gal tank is good for 3 fancy (fantail, oranda, any type of "double tailed fish") or probably just 1 common.
The rule of thumb here is a minimum of 10 gal. per fancy and 20 gal. per common or comet.

So technically with your group there you should get at least a 75 gal tank if possible.
Then the next thing that would be suggested is that you separate the common from the fancies.
Common's tend to be a lot more active and fast swimming than the fancies.
It would be the equivalent of keeping a cheetah and a house cat together during feeding time.
Okay maybe I exaggerate... but you get the point.

Some good places to look for tanks would be:
~ garage sales
~ craigslist.com
~ aquabid.com
~ Touch of Joy has had some luck with just people throwing out old tanks
~ they have some nice sales every now and then at pet stores
~ or even a temporary rubbermaid tub would be alright (though if you get a big one you might want to double up so that the tub won't start to bow out)

How often do you do water changes?
Is the one AquaClear filter the only one on the tank right now?
What additives/conditioners do you put in the water?

And again, I'm sure many people will come along and mention something similar to what I've said...
we mean no harm... it does sound a bit harsh, but we all just want to best for you and your fish.

Again, welcome to koko's! hope to see you around for a while!!

I belive you need a 60 gallon tank or bigger. Like Tinkokeshi said you co uld use a rubbermaid tub. Plus post pics or eles

So would I be able to use 2 30 gallon filters? Or do I need a whole new 60+ g filter?

I'll take some pics, I just have my phone though so they might suck haha

You don't need to buy one large filter if two smaller ones make up enough filtration. At least 10 times filtration is generally the rule with goldfish, so for a 75 gallon tank you need 750 gallons per hour filtration.

I looked up the aquaclear 30, and it only turns over 150gph, so in a 30 gallon tank, you are underfiltered for goldfish. Goldfish are really messy fish!

When I started I had a 10 gallon tank with only 50gph. After I found Koko's and got educated, I bought another same filter to make up the difference.

As long as you arrange the filters so the fish have a quiet spot in the tank to rest, 2 filters are fine.