If he is swollen all over and not just the belly area, then he has sustained damage to his kidneys, or heart, or liver, or all of the above, and fluid is accumulating in his tissues and abdominal cavity.
This can be due to a bacterial infection, or can be from damage caused by poor water quality.
With that many fish you probably have had levels of ammonia and probably nitrite that have caused damage.
Many of us have been there.... don't beat yourself up, but let's try to fix things for you.
First, I'd try to get the fish with dropsy into a quarantine tank. You can get another tank, a 10 gallon or one of those 5 gallon mini bows, (though a 10 gallon is best because most packaged meds are dosed for a 10, and it's just better; more room), or you can get one of those sterilite containers like Walmart has, put a heater and a filter in it and you've got a hospital.
You may need to euthanise your gourami, so I'm going to post a link to a very helpful article that details a very humane, gentle method. It's a sad task, but most of us here have had to do this for a sick fish that was suffering without realistic prospects of recovery. Putting a fish in the freezer is not humane, and it is believed to be a slow and painful death.
You need to go to the pharmacy or health food store and ask for
pure clove oil, also known as
eugenol at the pharmacy. Don't get toothache rememdy that has clove oil such as; Anbesol or Orajel. Those have other irritating ingredients and won't work in a gentle manner. Sometimes you have to ask the pharmacist because the store clerks or sales people don't know what you're talking about and will try to sell you toothache remedy.
Now, right away you need to be able to test your water yourself, and you need to get proper testing material. Strips aren't worth a plug nickel and are inaccurate and unreliable. They cost more in the long run, too. You need to get a good liquid test kit, such as; API Master test kit.
You need to test your water daily, sometimes several times a day for the first few months. You will need to do water changes as frequently and as big as is needed to keep the ammonia at 0ppm, the nitrite 0ppm, and once nitrate appears keep it at 20ppm or less.
Get PRIME by Seachem. It is a good low cost dechlorinator that removes chlorine and chloramines, but also detoxifies ammonia and nitrite, which is HUGE. While cycling a tank, and even once your through cycling, Prime can protect your fish from traces of ammonia and nitrite, and from big spikes that can happen due to a dead fish decaying that you didn't know about, or a piece of rotting food that you didn't see.
You still have to do the big water changes to remove the ammonia and nitrite because they are detoxified only for about 24 hours.
Prime will save your sanity and your fish's lives, and it won't interfere with the cycling process.
Don't add chemicals to raise or lower your ph, just let it adjust itself. Swings in ph from using ph up or ph down, etc., are much more harmful.
Don't over feed your fish and be sure to remove uneaten food after a couple of hours. You can use a turkey baster (dedicated to fish use only) to suck up excess.
A good routine of water changes with temperature matched, dechlorinated water, and a gentle vacuum of the substrate to remove excess debris, poo, uneaten food, mulm, etc., will help to keep your tank more stable and lessen the likelihood of ammonia spikes.
Unfortunately, your gourami with dropsy probably can't be saved so euthanasia is likely the best course, but if you could post a photo maybe we can offer a different recommendation.
If he is put into hospital, you can add 1/8 teaspoon of Epsom Salts per 5 gallons of tank water to help remove some of the fluid buildup in his body. (carefully dissolved before adding)
Please try to post photos of him, and your tank and other fish so we can help with other suggestions as needed.
Hang in there, don't be too hard on yourself. We've all been there with mistakes and bad advice from people we think should know what they are talking about.
AquariaCentral is a great place for you to learn about fishkeeping. Every one here wants to help you succeed and enjoy your new hobby.
These folks have hundreds of years combined experience and know soooooo much more that 99% of the people at pet stores... even small mom and pop fish stores.
For one thing... those folks in the business are motivated to sell you something and this flavors their perceptions and their advice, whereas these good folks here have no agenda except to help.
Here's the link to humane euthanasia.
http://www.aquariacentral.com/forums/showthread.php?t=148361
Let us help and support in any way we can. Keep your chin up.
