How often would I need to do water changes?Bristlenose Pleco get about 5" but would still at least need a 20 gallon tank. If you have algae it will eat it all pretty quickly. They also will benefit from Pleco wafers to ensure they get enough to eat. Wafers will sink and should be given at night just as you turn out lights. Plecos are largely nocturnal. They also have a high bio load, (poop alot) which adds to filter load, possibly ammonia buildup without proper water changes.
I have a 10 gallon but I’ve been told a clown pleco would be fine in a 10g. I can’t get a snail because my tank has openings on the top and they crawl out.What size tank is your Betta in? Plecos need very large tanks, even the smaller ones need at least 20g. A common pleco can grow up to about 2 ft. A clown pleco could go in a 20 gallon but since you said you want a tank mate for your Betta I'm assuming the tank is quite small. It may be best to do a snail if your tank is 10 gallon or under
Ultimately it is up to you what you decide to do. I'm sure a clown pleco would survive in a 10 gallon just fine but that doesn't mean it will thrive and be happy. With good maintenance and a careful eye on water parameters it should work out. Unfortunately bio load isn't the only factor that determines tank size for a fish. They can grow up to 4 inches and can feel cramped in a 10 gallon which is why almost everywhere you research will say they require a minimum of 20 gallon and an additional 10 gallon per additional clown pleco. That being said if you get a small one you can certainly keep it in a 10 gallon but upgrading it eventually to a proper tank size will make it much happier once it has reached it's adult size.I have a 10 gallon but I’ve been told a clown pleco would be fine in a 10g. I can’t get a snail because my tank has openings on the top and they crawl out.