[Franklin]

Right now I have a 45g tank, and am thinking about adding a 29g sump/fuge. Will that mean that I need to do water changes for a 75g system? Otherwise, how often and how much water should i change?
Thanks

[Ninong]

There are no hard and fast rules about water changes. Some people perform water changes every other week and other people perform them every other month. Some people change only about 5-10% of the water at a time and others change 15-20% of the water at a time.

Usually you estimate the total actual water volume in your entire system when figuring out how much you will need to change if you want to change say 10%. So, assuming you have live rock and a sandbed in your 45-gal display tank, it probably holds no more than 36 gallons or thereabouts. If your 29-gal sump/refugium runs half full, that's another 15 gallons or so. So maybe you would have a total of about 51 or 52 gallons of water in the entire system, including in the skimmer and the pipes. A five gallon water change would represent about 10% and a ten gallon water change would represent about 20%. I think that if you do a five to seven gallon water change every four to six weeks you will be doing just fine. If you have problems maintaining water parameters, then increase the frequency and the amount of the water changed each time.

Good luck,

[ick sucks]

yes i think so because when all the water is circulated through the entire tank all the water becomes one. thus to remove a percentage of waste by a water change you would have to do a water change for a 75 gallon aquarium to accuraltely remove what you want to in a 45 gallon tank. if you water changed for a 45 gallon tank and have a total of 75 gallons of water you would only be doing it for a 45 gallon. not a 75-wich is what your actual tank volume is.

[Ninong]

Originally Posted by ick sucks

a 75-wich is what your actual tank volume is.

How did you calculate that?

A 45-gal tank holds no more than 39 gallons of water when it is completely empty. That's allowing for the thickness of the glass walls and bottom of the tank and for the maximum water column in the tank and assuming no internal overflow compartments. Then you have to substract for displacement by live rock and sand.

His 29-gal tank/refugium would not run full. It would only run about half full, otherwise there would be no available space for overflow from the display tank during power outages.

Therefore, his maximum volume is less than 54 gallons before subtracting for live rock and sand and without adding in the small volume of water in the plumbing and skimmer.

There is no way that he has anything close to 75 gallons of water in his system, therefore he does not have to use 75 gallons as the basis for his water change calculations.

I hate to be picky but I don't thing we should allow misinformation to go uncorrected.

[Samper]

I do a 25 percent water change every saturday at the same time sucking out all the deitrus on the bottom and cleaning my skimmer. In a 20g with less than adequate skimming I feel it is necessary. I have very little algae problems, my inverts are healthy and happy, my pod populations are doing good and the water is crystal clear. I wouldnt recommend that everyone does something like this cause it does get costly but it's worth it to me.

[jiggly75]

I have a 90 gallon tank, 10 gallon refugium, and 20 gallon sump. My sump stays a little over half full. Once a month I turn the return pump off and let all the water drain from the overflow. That in return fills up my sump totally. So, I guess I do a 20 gallon water change once a month and all is well.