Water Changing! How Often?

[Clarke]

Here's some new questions...

I've had my 10 gallon tank + filter for about a week now. I've already done one 10% water change (with treated water, of course). My questions:

1. How many water changes should I do a week?
2. Should I use the Gravel Vac to pull out water/clean rocks at the same time?
3. When do I do a "complete" water change?
4. Does doing a complete water change mess up the nitrogen cycle?
5. Anything else I should know about water changing?

Thanks for all the help everyone. I've learned so much here!

[adiumroot]

1. Depending on the tank's bioload (number and size of fish). But the usual is 15-20% once a week. If you see that the tank is still dirty, then try 10-15% every 4 days. Just make sure that your filter is just the right size/power for your tank.
2. Well, a gravel vac siphons out water to clean the rocks. That's its job. Count the water it draws out as the water you need to replace.
3. Do not do a complete water change unless in emergencies or a very severe disease outbreak (note the "very severe"). An example of one such emergency is if a chemical accidentally falls into the water and you get your fish out in time.
4. AFAIK, the complete water change does not mess up the nitrogen cycle. What it does is it stresses the fish out and they have to adjust to the new water immediately. You can lose fish this way.
5. Hmm, I think I've covered the basics. It seems you know about the nitrogen cycle already, so that's good.

[Nataku]

If it's only been set up for a week it isn't cycled yet. Do you have fish in this tank already? Or are you doing a fishless cycle?
If its with fish, you need to be doing water changes to prevent the ammonia (and then nitrite) levels from spiking so high that they ham your fish (if these are fish you plan on keeping). How often depends upon the bioload of the tank and how fast they are causing the parameters to spike. You should be testing the water daily and doing water changes based on those results.
If it's a fishless cycle, you don't need to do a water change until the tank is cycled.

Yep, gravel vac is what you'll use for water changes if you've got substrate. The purpose of a water change is to remove the ammonia and waste build-up. The gravel vac is designed to help you get at all that waste, which will fall down between the rocks and other wise be impossible to get at.

If it's a cycled tank? Never. Doing so generally screws over the cycle, causes the colony to go into shock, and can kill it off. The 100% water change itself isn't what destroys the cycle (since most of those bacteria will be house in your filter and substrate, not free floating in the water) but new, clean water being placed in that has no waste build-up whatsoever for them to feed on. You only break a cycled tank down completely if there was some really bad disease outbreak in it. Sorry, if that's the case, you destroy your cycle and start over, otherwise you are just too likely to destroy the new fish as soon as you put them in.

See above paragraph.

Common sense is your friend? Have that and you should be good. Never stick your hand in a tank if you've got an open wound on it. Have lots of towels handy. If your substrate is very fine, or your filter is very strong, turn it off or lower its setting when stirring up the substrate to prevent so much of it getting sucked up into the filter. Picking gravel bits out of your filter because you didn't is not a particularly fun experience.

[adiumroot]

@Nataku
Thanks for clearing that up. I got confused a bit there. But nonetheless, a 100% water change should only be done in emergencies.