Are they goldfish in cold water or tropical fish in warmer water? Doesn't really make a difference - they both have to be cleaned out. If you have a gravel cleaner - use it to get the dirt out of the gravel. A gravel cleaner is a syphon that can be used to clean the gravel and take out the dirty water. If you haven't got a cleaner, then stir up the gravel with something - your finger or a stick. The dirt will start swirling around. Take out the dirty water with either a syphon or a jug. Leave the fish in the tank - as long as you don't take out 100% of the water, they'll be fine. Once you're satisfied that you've got most of the dirty water, prepare new clean water. Make sure that it's approx the same temp. as the water that you removed. Use a dechlorinator according to the instructions on the bottle. Before you add the new water, clean down the inner sides of the tank to get rid of any algae (if you haven't got any fish that will clean it for you) Put the new clean water in the tank - carefully. That's it. Most probably the water will look a bit murky to start with due to the disturbed dirt (it's impossible to remove 100% of the dirt) but it will settle quickly.
Oh, BTW - welcome to the best fish forum on the net. Also the craziest
Hi Phil
You sound as though you're a young fishkeeper-are you? Nothing wrong with that, the younger you are the more you will grow to enjoy your hobby. Some of us may think it's cruel to fish keep as it's taking fish out of their natural environment. Just think of it this way, most of the fish that you encounter will have never seen the real world in their lives. So don't worry about it. You will encounter big words like filteration and technical terms such as the nitrogen cycle, ammonia levels, Ph.Kh etc. If you do and you don't have a clue-don't worry. It'll all be explained piece-meal so that you can understand it. Most of all this is a hobby to be enjoyed. You WILL come across a few trials and tribulations, the word is PERSERVERANCE.
I hope you will be happy with your hobby and a warm welcome to the forum. The name of the game is to enjoy.