you don't save betta's from cups by buying them...see the stores put them on the shelves to sell them, and they put them there at a price at which they'll make a profit. So if customers purchase them, then it would make sense that since the business is making a profit and will probably be sure to restock the item, hence putting more bettas in cups. If people would let the existing bettas in cup just die off then the businesses may realize that their customers aren't okay with purchasing a product that has been cared for so poorly...and then care for it better. Furthermore...they would be taking a loss by stocking a perishable item that doesn't sell...hence stop stocking it. I'm not saying "don't buy betta's in cups" I'm just saying its not going to help the plight of bettas in general. I'm sure that particular fella will be most appreciative, both mine are
But yeah, you can always drop a frozen shrimp in the tank, or even just feed it fishfood daily to keep the biofilter live...fish aren't the only source of ammonia in the world. Hell you could even plant it. But by all means, do one project at a time, having multiple tanks unstable at a time can be exactly what gets you burnt out on fish keeping....just too much to keep track of.