my fishkeeping woes

Question
ok for many years now, i have been fish keeping but everytime, my fishes keep dying from disease or some other reasons...the bottom line is, they jus keep dieing even though my ammonia nitrite and nitrate lvls are all good..that is ammonia 0, nitrite 0 and nitrate 10-15 ppm..i have a 20 gall tank with a cycled HOB filter with a bio wheel...my tank is also planted...my few questions are :

1) how to prevent fish diseases?
2) how often to do water changes and by how many percent?
3) do i need to vaccum the gravel to suck up the fish poo or jus lift the water siphon tube in the water?
4) what to do when fish is sick
5) how to check if fishes are healthy at the store.

and finally...

6) what should i do when bringing new fish home?

pls help me as much as possible ..thanks

Answer
Hello Charistance,

For your first question there is many answers. first off you can have the temp. to high or to low (around 72 degrees F.). Also you need to do a 25% water change every week to insure clean healthy water, as well as make sure you have clean filters constantly. Every time you do a water change add about 1 1/2 tablespoons of aquarium salt to your tank THIS IS A VERY IMPPORTANT STEP. Another important thing is to make sure you dont over crowed the tank.

Also you don't need a gravel vaccume just get a normal water tube and use it to make water changes. If the fish are sick you just have to try and keep your water in good condition just like normal and add another 1 tablespoon of salt.

To tell if the fish are healthy out of the store you want to find one that moves normaly (like the rest of the fish in that tank) and that is active alot. Also dont get one with any scrapes, marks, or red gills.Also alot of the stores will help you pick out a good fish. But in general I would use these tips, although they vary from fish to fish.

Look at the top and sides of the tanks. If most are encrusted with residue, look for another shop entirely.
Look for clear water. If it's discolored, avoid that tank. If the water in most tanks is discolored, look for another shop.
Scan a half dozen tanks to see if any fish are sick or have died. If you see more than one sick or dead fish, find another shop.
Avoid tanks with decaying plants, as the water chemistry is questionable.
Do not buy fish that just arrived in the shop. They are stressed from travel, and might be carrying disease.
Avoid fish with cloudy eyes, torn or clamped fins, and spots or sores on their body.
Avoid fish that are sluggish or appear to be shivering.


Thanks for your time,

Michael M.