I totally agree with Chris! How many litres is your tank?

I think you should definitely buy a filter and cycle the tank with the two fish you have in there (depending on how big the tank actually is). If you keep a smaller bio-load until your tank cycles, you'll have much less headache for sure. Overstocking tanks greatly increases the likelihood that the entire thing will crash and most or all your fish will die nearly instantly. I've had it happen before and it really sucks. I put three guppies in a 9 litre cycled and established tank that previously held only one betta fish and they literally died hours after their first feeding. Even though the tank was established (naturally planted and running for over a year), it previously held a much smaller bio-load and couldn't break down the excess ammonia fast enough.

Also, overstocking the tank highly increases the chances for fungal, bacterial and parasitic infections that could be passed onto your snakes. It might be just me seeing the tank as smaller than it actually is, but if you want a sustainable source of food for your snakes, I would go bigger and have the tank cycled before adding fish. It's best to do it right the first time than to have to spend more money later on trying to fix it.