Reddit reviews Karen Low 25 Watts (Tank Size: 5 to 8 Gallon) Adjustable Aquarium Heater Anti-Explosion Submersible Fish Tank Water/Temperature Range 18~33'c (65°f and 93°f.)

tl;dr (the whole thing, only the first page) I will donate and mail at my cost a brand new 25 watt submersible heater that is good for tanks 3-8 gallons and a digital thermometer for this betta. I use one in a 6 gal and a 3 gal and they work great.

thermometer

heater

PM me if you think it's needed.

Petco dollar-per-gallon sale,you can get a 10 gallon tank for $10. Best deal around. Depending on how many bettas you have, you can get a 10 gallon tank and divide it in half to house 2 fish.

Sponge filters are the cheapest, this is the one (#11) that I have in my 10 gallon divided tank. Works great. You'll also need a small air pump, those you can find at the pet store for like $5-10. Here's a cheap one online.

Get an adjustable heater, not a preset one. Heaters aren't too expensive. Here's a really cheap heater for a 5 gallon, if you do a divided 10 gallon you could get 2 and put one on either side, keep them on a low setting. Get some glass or digital thermometers, not the stickers, the stickers are really inaccurate and hard to read. These glass ones are only $2.

For plants, /r/Aquaswap tends to have the best prices. I've gotten a good amount of plants there. Most pet stores or an LFS if you have one should also have at least a couple aquatic plants.

Since your filter setup will be new, make sure to also get a water quality test kit and carefully monitor the parameters until your tank is cycled. Cycling a tank is THE most important thing for keeping any kind of fish healthy. An uncycled tank or a tank without a filter has the potential to cause serious damage and even death within days.

Here's a really nice link that will explain how to cycle your tank.

Sorry this probably seems like a lot, but I swear it really is necessary. It gets easier as you go. A lot of it is the fault of pet stores and big companies that try to relentlessly push the "betta bowl" fad and don't acknowledge at all how terrible it is to the fish. It's really great to hear that you're doing your own research now though and want to improve the lives of your pets! It's always awesome to hear about the poor "bowl bettas" getting upgrades to real tanks!

This is my copy and paste from another thread, so if there's a few assumptions it's not pertaining to you, but I have everything you'll need in this!

You're going to need a 5.5 gallon in order for him to thrive, otherwise you're gonna have a very unhappy fish who might live but will not be doing good. An aquarium is a tiny ecosystem in an enclosed space, so a .5 gallon gets very toxic, very quickly. It'll hurt his gills, it'll hurt his fins, just everything. The ammonia will buildup quickly and reach very dangerous levels, and although 100% water changes will decrease that, an established bacteria colony (made up of harmless ones) needs to be there for the fish to really be healthy!

When you see a happy and healthy betta, you will never want to go back!

Cheap quick solution for now: Five gallon Rubbermaid from Walmart, this filter, paired with this air pump, and this connector tube. It will run you about $20, and can hold for a while! This heater works so well and is the cheapest you'll find anywhere!

Long Term: Buy a 5.5 standalone aquarium tank from Petsmart (only $14.99) and a little pack of gravel, and some live plants of your choice! Check our r/aquaswap for some cheap plants from other Reddit users. Just move over the filter and heater, and you have the perfect set up! There are also some cheap lighting solutions that you can buy to help your plants grow!

Everyone gets tricked in the beginning, but making steps towards helping your betta will enhance his life so much! The whole set up, the filter/air pump/tubing and tank from petsmart, will cost you $35.59!