tanks is 36' inches x 15' wide and 20' tall. I have only 6 fish(4 barbs and 2 alninos)
Its the petstore cuz after the last 1 died I bought another green barb at another petstore and this one is doing gd but everytime i buy green barbs at the other pet store it would die. i really dont check the nitrate or ammonia level...I use my instints
instincts

hmmmm yes you can use them to tell you when to test the water, but having a good look at the tank is hardly going to give you a reliable answer as to the water conditions in your tank.
go test your water.
yes i should, just some ppl dont use the testing kits but use their instints...First wash your hands with soap and water, then carefully rinse all the soap off your hands. Put the tips of my fingers in my fish's water and move my fingers quickly back and forth to produce bubbles on the surface. And if the bubbles sit on the surface of the water and not pop quickly..it means it not gd. Ill check to see if the water is cloudy, or foamy, or has an unusual odor, and look at the edges of the surface of the water near the glass. Cloudy or Foamy water often does not smell good. Rather it smells like garlic or cigar smoke. The smell is often an important clue in helping to decide whether the water is good for fish or not good.