Okay thank you! Currently, both of my axies are out of their tanks and I just rinsed their filters and added new replacement cartridges. They both have HOB filters. I also have bubble bars going full blast in each of their tanks. I have sponge filters as well but I have removed them from the tanks. Do you think they'd help if I put them back in and turned them on?
I hate attached an image of the filter guard before rinsing.. that's what it looks like
Ya that looks just like the slime in the pictures.
The sponge filters would be fine to go back in, but maybe not until the levels have stabilized and you've seen no sign of the film. The sponge filters reduce oxygen, which is fine in a stable tank, but right now you need all the oxygen you can get. What media do you use in your HOB filters? Ideally you'll want several different levels of filtration media, biological, chemical, and mechanical. It sounds like between The HOB and sponge you are meeting the requirements. As long as you're cleaning all waste everyday at minimum, the bacteria should be able to be contained.
If you get a larger tank to combine your axies in the future, I'd recommend upgrading filters to a canister. I'd purchase from Amazon, because the pet supply shops charge nearly twice as much. I have a Cascade1000, I paid less than $80, but petco was charging $150. For 10g there's no need for that power though, just if you upsize later.
So for now, my advice would be to first test your water with that kit, then if levels are high start doing 25-30% water changes daily, and test everyday before water changes. Once the levels are within safe range, stop doing daily changes, go back to 25% weekly. You can also put the sponge filter back in at this time, but I'd suggest replacing the media in it, starting fresh.
Then just watch the tank, keep test every other day, to check for changes, and also for the cloudiness/slime. Cloudiness won't always be a bad thing, it's when the bacteria doesn't level out that the cloud leads to slime.
Also keep checking your filter media for any sign of slime throughout this process. I might suggest getting some fluval bio rings, or similar product. They will help with biological filtration without reducing oxygen while you're keeping the sponge out. You can just put some in a piece of nylon stockings, or a mesh bag, place it somewhere in your HOB filter.
Keep your axies out until you've had about a week of near constant safe levels. Then it's just about keeping waste cleaned up, testing water weekly, and 25% changes every week. Clean your filters every couple months also.
Always make sure their water temp is in the 60°F-67°F, ideal would be 60°F-64°F, but that is quite hard to achieve without an expensive chiller. My water is usually 64°F-66°F, I just use frozen water bottles filled with dechlorinated water, switching them out throughout the day.
Sorry for these really long replies, just trying to include all the info I can think of.