Cleaning Fish Tank

If you added all the fish at the same time, they definitely died because the tank wasn't cycled, plus with all those fish you had, you probably overstocked the tank, which compounded the problem by leaving the fish with too little oxygen. A cycled tank means that it has enough bacteria that will convert ammonia (a major fish waste product which is very toxic to fish) to nitrite (also toxic, but less so than ammonia) and then to nitrate (far less toxic to fish than ammonia or nitrite). It takes anywhere from 4-10 weeks for a tank to "cycle" and build up enough bacteria to efficiently process the ammonia to nitrate. Your tank should be cycled by now, so your survivors should do better, for now. Because your guppies are breeding, your tank will be overstocked again soon. A ten gallon probably can't handle more than 12 adult fish of the types you have (adjust accordingly to accomodate babies.) As for what to do about cleaning, keep it simple, just do partial water changes, volume and frequency are up to you. Here is where a test kit would help because it could tell you how much you need to reduce your ammonia, nitrite, and nitrate. If I were you, I'd do daily 30-40% water changes for the next three days, then go to doing one of those once a week. Get a small, simple siphon gravel vacuum (you don't need anything that is powered) and when you take the water out, suck it out of the gravel so that you remove some feces and uneaten food. DON'T use soap or vinegar or anything to disinfect anything, not for this. You WANT bacteria right now, even algae can be helpful at this point by sucking up your ammonia. To sum up: Don't clean your filters (at least not yet), don't disinfect anything (you don't have a disease problem), do patial water changes, and you can vacuum the gravel (but not with your household vacuum!). Remember to use a dechlorinator, and some of those have ammonia and nitrite neutralizers in them (like Prime) which will help your fish survive any further spikes in toxins. Also, sell some of your baby guppies before you have 20 fish in your 10 gallon tank (definitely overstocked), or get another tank for the babies (that's what most hobbyists do). You have a very small tank, it can't support a whole lot of fish and don't get anymore plecos, they'll outgrow a ten gallon in no time! Sorry this is long, but if you understand what cycling is and that you need living bacteria in your tank to process toxic fish waste products, its easier to understand all the advice you're getting from everyone here.