The first thing you need is a good water test kit. Orandas/Goldfish are messy and really turn the water in a new tank. Test the water everyday because ammonia and nitites are really bad for them. You want zero on both and it won't be until the tank is cycled. The minimium for gold fish is 10 gallons each while they are small and more when they get big. 4 ten inch fish would need 100 gallons or more to really be ok. Get a bio wheel filter if you don't already have one. For the first month expect to change 5-10 gallons a day. I've had orandas and other goldfish for a while and they are a lot of fun in a tank or pond. They are very friendly and always hungry so don't over feed them. They are carp and are built to eat all the time and will always look hungery. It's OK if they don't eat every day because overfeeding is worse. The pond forum talks about goldfish a lot.

Unfortunately, your tank really is too small for 4 goldfish of any type.

With proper care & feeding they will grow quickly - although the rounder-bodied goldfish do grow more slowly than the streamlined types. With a tank your size, you will have to do a LOT of water changes to keep the environment under control. Even that may not ultimately keep them alive.

I would suggest a 55-gallon tank for your 4, or at least another 20-30 gallon to transfer 2 of them into.

As an example I'm borderlining with three ryunkins and I have a 350 bio wheel filter with two bio wheels, a Whisper 30, and a fluval 304 canister filter packed with Bio media. This is in a 29 gallon tank and it's working but as they grow I'm going to be in trouble and I have had Nitrate porblems. Use Tetra Nitraban in the water and it really helps out a lot. My fish are headed for a pond later this year so it's only a temporary home for them. I change 5 gallons everyday just to be sure. If you don't keep the water in good shape the orandas will get sick, Ick or an internal infection and then it's pretty much over if you can't get the water straight. Look at your fish now and know what their spots, color, fins, and any other characteristics are. Pay attention to changes in behavior, sitting on the bottom, staying at the top, gasping, fast gill movement, or clamped fins. Pay attention to when and how much they eat. This way you can see if there are any changes in behavior. I don't know how people keep a few goldfish in a bowl and never change the water.

I always find it so distressing to see the fish stores stock their tanks with like a ga-zillion goldfish! They all move slowly and sluggishly. :( My orandas are soooo active!! It's amazing how quickly they swim around when they're in a big tank with good water quality.

Puddlemaker is so right about behavior. Fancy goldfish are as active as koi and comets! They shouldn't ever be just sitting on the bottom or moving sluggishly or slowly.

I think your aquarium may be okay for now, but you likely would have to go bigger in the future. Also, I don't know how much you know about the "nitrogen cycle" but perhaps do a search on the internet, or use words like "aquarium nitrogen cycle" and you may find a good article or two. I have attached a link for starters.

Basically, fish eat food and produce ammonia as waste. In an established aquarium, there is beneficial bacteria which grows on the filter and the gravel which eats the ammonia, converting it to a slightly less harmful thing called nitrite. Another bacteria then eats the nitrite, converting it to the even less harmful nitrate. You then control the level of nitrate by doing regular water changes perhaps weekly.

The immediate concern is that because your tank is newly set up, the beneficial bacteria don't exist or at least don't exist in large numbers. They will grow naturally. However, the amount of waste produced by adding 4 fish at once may be too much. If it is, and the bacteria can't handle all the ammonia, the ammonia level will build up, possibly harming the fish.

That's the reason it's good to get an ammonia test kit. Also nitrite too and nitrate wouldn't hurt. You can monitor if these levels get too high do water changes if they get too high. You may have to do water changes daily for the first bit, depending on what your readings indicate. You just change maybe 20% to 50% of the water using new tap water, at the proper temperature and dechlorinator added to it. At first you may have to do these daily and that may get frustrating but hang in there. Once the beneficial bacteria grow in the tank to acceptable levels they will be able to handle the waste the fish produce and the ammonia reading will read 'zero'.

Then you may find that the nitrite level goes up, here too you need to do water changes if it's at an unsafe level.

Anyways, there's alot to it, but this article explains it fairly well. Don't be scared, it's really not as bad as it sounds, and understanding how it works helps alot in knowing what to do for your fish.

Here is a link that might be useful: Nitrogen cycle

I think a very good and informative website/forum is www.kokosgoldfish.com

Yesterday after having my water levels tested. I added a small red cap oranda to my aquarium where I already have 2 orandas and 1 Black Moore (which I have had for about 3 weeks). They are in a 55 gallon aquarium and I will not add any more. I believe they are all young the largest being 2.5 inches. I was surprised at how quickly she seem to adjust eating and swimming with the others no hiding or sitting at the bottom of the tank. I fed them this morning and they seemed fine. Later to my surprise my black moore seemed to be following her around budding her backside with his head. This didn't last long. Later I noticed my larger Oranda doing the same but for a longer period of time and more aggressively. I notice there water seemed warmer than usual so i added a few ice cubes and turned off the lights (I've never done that before). I also changed the artificial plants around in case it is a territorial thing. Should I be concerned about this behavior?