It is almost impossible to get rid of snails, unless you add some copper or a botia (snail eating fish). Snails have their place in the aquarium; they eat all of the food missed by the fish. The mulm on the bottom left from their waste is a great place to harbor good bacteria. The snails always find there way back usually, plants, gravel, digestive tract of the fish, etc If you keep some of your old water from the tank and add it within a day, then you can add in fresh water as long and the ph and temperature is not too different from what the fish are use to. Endlers can be fussy at times, so I usually add new water by dripping is in with a siphon with a valve to reduce flow or just double the water each time you add fresh water. For example, you start with 1 gallon old water and add 1 gallon fresh, next hour you add 2 gallons and so on. When I acclimate my fish it takes me over 24 hours, just because I am paranoid.