Use the test kit that came with the 120 as long as it's not very old. Otherwise invest in a new one. If you have a pocket of toxins in the sand in one tank it doesnt mean you'll have it in an other, right now. Trumpet snals are great for burrowing through the sand and keeping it turned preventing and anarobic condition from delevoping. They do multiply quickly though and can become more than you want just crush them and let the fis eat them. They don't bother anything or eat plants. Just check everything and or like I said let the LFS do it for you. You do use a declorinator at WCs, correct? You can also check your tape water with the kit so you have a base line reading of what's going into the tank.