I agree with the above ladies.
I would add, though, that you need to keep well and truly on top of your maintenance regime. 12 neons and 3 guppies in a ten gallon tank is somewhat overstocked, so nitrate will build up very quickly. I would say you need to be changing at least 50% weekly. Similarly, if anything does go wrong, an ammonia or nitrite spike will be a problem much quicker in your tank, so make sure you test the water regularly, at least monthly, and immediately if you spot any potential signs of trouble.