You need to get a testing kit, you also need to learn how to properly stock a tank. Also, fine gravel/sand isn't going to solve your missing fish problems, keeping a list of your stock, checking your stock daily and basic care will solve 90% of your problems. It sounds like you don't take care of your tank properly, that's all.
Why would you ever put a rock bass or even a MUSKIE in a 29g tank?
I can't believe nobody has lost their mind over that yet. I don't want to sound harsh, but you are completely overstocking your tank(s) and if taken care of properly you should suffer little fish loss. You should never own any size aquarium without all the proper testing kits you need to do at home!
Would you buy a dog & never take it to the Vet for it's shots, heartworm, etc? No. Do the same for your tanks.