(If you are here because of problems with your tank or trout, please visit Troubleshooting.)
With the trout in place, keeping the tank bacterial colonies happy is the most important job. The nitrifying bacteria in the tank change trout waste (ammonia) into nitirites and then further into nitrates. Nitrates are eventually converted to nitrogen gas. While ammonia and nitrites are fairly toxic to the fish, nitrates are not very toxic at all.
Most of the nitrifying bacteria are surface dwellers. They live on all the surfaces of the tank and equipment, and especially on all faces of the gravel. Vacuuming the gravel will remove debris that could eventually suffocate the good bacteria (or create other problems) if allowed to remain.
In vacuuming the gravel, you will also be removing water. This removal is usually sufficient water change for your tank. Replace all the water you siphon out with tap water treated in the bucket with a TapSafe compound. As you add the new water to the tank, monitor the tank water temperature. You may need to add the new water in stages, so as to avoid wild swings in temperature (which will stress the fish).
The removal of dead and visibly sick fish is also important. Many fish start to get lethargic, or have problems swimming. Some never learn to eat. Eventually, they simply float around the tank. These fish are sick, and they will never get better. One dead fish body, if left too long, can spread the disease to the other fish causing damage to the whole population.
Trout should be given small amounts of food. Overfeeding the fish can pollute the tank environment. Give only one pinch of food at any time, and remove all the extra food particles. Trout do not need to be given food daily, but as long as the amount is small, up to 2-3 daily feedings are acceptable. The trout will seem “hungry” all the time; remember that they are wild animals, and their instinct is to eat any food presented to them, no matter how often. These trout can survive over a weekend without any food, but during vacations it is best for someone to check on the tank and provide a small amount of food on a regular basis.
Use your pH and ammonia test kits to check the water conditions regularly—at least once a week, but more often is better. Test should indicate a neutral or near-neutral pH (in the high 6s or near 7) or slightly alkaline (in the high 7s or low 8s). Water that is acidic (below pH 7) or VERY alkaline (above pH 8.5) can cause problems with fish health. Above all, the trout need a stable tank pH. Large changes in the pH can stress the fish.
Ammonia levels are best as close to zero as possible, though a small amount of ammonia is inevitable. You want ammonia and nitrite levels remain consistently low (preferably under 2ppm, and definitely under 4ppm for ammonia, and not too much higher for nitrite), and that your nitrate levels will rise. This simply means that the bacteria are doing their job. Eventually nitrate should level off, also as the bacteria do their work to turn it into nitrogen gas and allow it to bubble away. (You can read much more about ammonia on our all-about-ammonia page.)
If you are not sure about your levels, watch your fish. Are they happy? Do they swim around, look for food, or hold a constant place in the tank? When you put food in the tank, do they respond enthusiastically? Some trout are adventurers, and others are homebodies, but as long as you have some of each, and they are spread throughout the water column (some at the top and some at the bottom), that is good. Eventually you will know what sorts of water chemistry your trout can handle--it is never the same for any two tanks.
If fish behave strangely or start dying in large numbers, poor water quality is often the root of the problem. This is where a large, gentle (slowly adding the new water in) water change would be called for.