Iron waffle

How often and how much is it recommended to do water changes on a fully stocked aquarium? I've heard from 50% every other day to 10% every two weeks.

Shawnie

it depends on if its overstocked, filtration, and type of fish etc? my 75 gal has oscars, convicts, dempseyts and is overstocked and has a filter for 1200 GPH but I still have to water change it every other day of 50% to keep my readings prestine..but my 55 gal which isnt overstocked, I change about 50% once a week..

Iron waffle

Ok, thanks. I have a lot of small fish. Would 7 1" tetras produce the same amount of waste as a 7" oscar? Is there a rule to the size of a fish and its bioload?

Shawnie

heck no...your tetras would take probably a couple weeks to hit the same bioload as my piggy oscars give off in a few days..but a goldfish is close to an oscar as far as waste in a small tank..does that make sense? each fish has a different bioload so depending on what you have and the size of your tank depends on water changes

Iron waffle

Thanks Shawnie, good to know. I'll be cleaning the goldfish tank more often

DarkRevoultions

Gilbert,

I have a 29, 200, and 350 gallon tank and I fill the water up to the top, and I usually siphon the tank and get the water level down to 1-2" and then fill up the water. I usually think of it as a water change/siphon

If you siphon the tank you have once a week, or every few selected days. Just don't siphon the tank once a month, because it's going to be real bad.

Peterpiper

Hi Gilbert,
The reason that we do water changes is to remove the nitrates that remain in the water after the bacteria have done their thing.
The amount of water that needs to be changed will depend on the bio load, amount of plants and the filter system you are using in your tank.
The only way to know how much water to change and how often is to test the water.
I don't know your setup. But lets say you are aiming at a nitrate level of no higher that 20
Now before you do any maintenance ( weekly ) test the water, and write down the readings, let say you have done the tests and have the following.
ammonia-0, nitrite-0 and Nitrate-20.
Now you do the syphoning cleaning etc, and you have removed 10% of the water, you now replace the water. One week later you test the water again, and get the following readings.
Ammonia-0, Nitrite-0 and Nitrate-25.. Now you know that you did a 10% water change last week, but your readings for nitrate are higher than your target (20). increase the water change to 20% this week and keep testing every week and write down the readings. you will soon find out how much water to change each week.
Pete