Your tank is massively over stocked.
In My Opinion Common Plecos aren't suitable for any tank under 100 gallons long term for a few reasons. They get to be 24 inches long which is very large, they have a very high bio load when fully grown and would have a major impact on all fish within the habitat due to ammonia, males might harras other fish during breeding season that enter his territory, and fully grown adults are known to eat smaller tank mates such as the ones the sizes of neons. They also will literally outgrow your tank
Mystery snails proudce a tremendous amount of waste and will negatively effect any type of living creature in the tank if the proper water changes aren't provided. I would recommend returning this snail as it will spike your ammonia levels
Your water changes don't suffice. In anything less than 5 gallons you should ideally do 1 50% and one 100% water changes weekly to minimize ammonia, and nitrites content. In a A tank of that size you shouldn't have to worry about nitrate/nitrite poisoning as nitrates/nitrites are both a result of bacteria oxidizing ammonia into those substances. Cycling doesn't occur as much in tanks less than 5 gallons. In a tnk upwards of 5 gallons. It has the ability to hold a stable cycle, and depending on the stocking. You should do 25-50% water changes. As 100% changes can slightly impact the cycle
As for the bloating.
Originally Posted by DarkMoon17
Swim Bladder Disease (SBD)/Bloat
•Symptoms: Betta has trouble swimming, maybe he can’t stay upright and can only swim on his side.
•Treatment: This is not a contagious or fatal illness. If it isn’t congenital (aka a condition that he/she has had since birth), then it is caused by over feeding or feeding the wrong foods. Bettas will typically recover after a day or two of Epsom Salt treatments (1-2tsp/gal) and fasting. You can help prevent a reoccurrence by switching to a better pellet food, feeding less and offering a more varied diet. To make it easier for the betta to eat and breath, you can make the water shallower. You can offer him/her frozen daphnia (sold at Petsmart) as daphnia will help him/her pass stool. DO NOT FEED THEM PEAS.
The Four Most Important Aspects of Betta Care Are:
1) Proper Water Changes
2) Warm Water (78*-82*F)
3) Varied Diet
4) Quarentine New Fish/Plants/Tankmates
If you do these 4 things, you can greatly reduce the chances of your betta getting sick.
Things to keep on hand at all times
•Extra nets and 1 gallon containers
•Aquarium Salt (Aq.Salt)
•Epsom Salt (ES)
•Potassium Permanganate (PP)
•Quarantine tank (QT)
Before you treat your fish for everything under the sun, check the water chemistry. Toxic levels of Ammonia, Nitrites and Nitrates are extremely harmful and weaken your betta's immune system resulting in illness. Many petstores will test your water for free. Liquid tests are much more accurate than strip tests.
•If your fish look like they are lethargic, gasping for air or are swimming head down do a water change immediately because they probably have nitrate, nitrite, or ammonia poisoning. Do not use chemicals to remove them as they are ineffective. Prime does remove nitrites/nitrates but it is still most effective to do a water change.
•Extreme pH variation can also cause illness. Sand and porous rocks like sandstone or lava rock make water more basic (>7.0) while Indian almond leaves, peat moss and oak leaves make the water more acidic (<7.0).
•Are there chlorinates in the water? Did you forget to add the water conditioner? If so, quickly add your water conditioner!!
•Many issues can be cured by a simple water change so it should be the first thing you try.
Conservative Treatment Versus Medication:
There are two ways to treat a sick fish. One is the conservative route. It involves increased water changes and (usually) salt treatments. The other route is using medication. There are some illnesses that respond better to medication than water changes and salt, however most illnesses can be cured simply with a bit of TLC and salt. In general, you should always attempt conservative treatment methods before using medicines as medicines can be hard on your fish’s internal organs and over using medicine or not completing the treatment cycle can result in the creation of medicine-resistance bugs.
Therapeutic Additives:There are a number of things you can do for your betta to reduce stress and support their immune system. Indian Almond leaves, tannins, black water extracts, and peat moss pellets are all things that you can add to help prevent illness or help recovery. API Stress Coat and Kordon’s Fish Protector are water conditioners/additives that help slime coat production and skin repair. They can be added at any time your fish shows signs of illness..