I have a 40 gallon tank bare bottom with a over the back filter. I have just some rock with 10 crabs and 5 snails. I have it set up just get my rock cleaned up that I bought everything from. The tank looks fine for temporary use until I move to set up the 125. The 40g has been up for about 2 months. When I first set up the 40 should I have done water changes right away? Should I have let it cycle? Can you explain the cycle briefly?