Awww so sad for me.
I could not resist the cuteness of the frogs, and now no shrimp for me. I wonder what this would do for any prospective algae/leftover food/refuse.
Clean your tank frequently. Good filtration should prevent food and waste build up between your water change cycles. If you see an excess of food waste in your tank, feed less. If there is an excess of waste ( not un-eaten food, fish waste ) you can increase your tank circulation and have a power head run parallel to the substrate to help lift off the waste so it can make it to the filter, or you may need to increase your filtration, or add more physical media to your filter.
I may one day make a species only tank for them. For now they are communal. They are adorable! They make me crack up.
I understand I need some MTS to aerate my sand and now I have assassin snails which would eat them. Bleah. As a newbie, I think I am like...making interesting choices. How do I avoid anaerobic bacteria build up in my sand now?
As long as you keep your substrate under 3 inches or so you should not have a problem with anaerobic bacteria. But if your substrate is deeper, and is sand as you say, when you are doing your weekly water change you should mix 1/4 of your substrate up, so if your sand substrate is 12" long you will turn 3" of it a week. Just do a light mix, google "how to fold in egg whites" I know that's for cooking but the general idea of the "folding" method works great on sand substrates and does not make a mess of thins, I used to do this in my cichlid tank when I had them.
For the snail, you can still get MTS and pond snails, and it's probably actually an even better idea that you get them since you already got the assassin snails. The assassins will keep their numbers in check, if you have a second tank or are able to even keep a small plastic container with some sand in it with water you can keep some of your MTS on the side so you never completely lose your stock. MTS and pond snails are asexual so they will reproduce on their own, and can do so very rapidly. I have MTS and pond snails in all my aquariums ( probably ) but you hardly ever see any because I keep the numbers in check, by not over feeding and good water change routine. MTS and pond snails are often free , just go to your local big P pet store and ask for some, their aquariums are usually filled with them and if you get a friendly and patient person to help you, you can get a lot of both MTS and pond snails for free, if you don't live next to a store like that you can usually find people on here with them for next to nothing. I sometimes see people RAOKing them for the price of shipping.