# Questions on water changes



## Sully (Oct 31, 2012)

Would like to hear any/all opinions or thought s water changes. Do you take into accountthe size the tank can hold or the appriximate volume of water in the tank after all live rock, substrate and any thing else that would displace water?

For example, I have a 20 gallon set-up with approximately 20 pds or so of LR and about a 2-3 inch substrate of sand. I'm no physics major (or minor for that matter) but my guess would be that I only have about 15 gallons or less of water when my tank is full. So do you do your 10/20/25 or 50% water changes based on empty capacity volume (bare tank) or by actual water volume in the tank (full of whatever you've placed in it)?

Do the same principles apply to freshwater? (for whichever way you answer with)

If this is a dummy question, please be kind in the bashing.


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## coralbandit (Jul 29, 2012)

I started a thread a while ago about peoples water change habbits. Many responded.Hit my name ,search threads started by and find,lots of good ,different input.I like to change about 50% in a month on my reefs.Totally unecessary according to test,but I don't need to add supplements to tank as they're are replaced with regular changes.15/20 g in the % game don't add up to a couple of gallons so do as you will, but keep track so if change is necessary(due to water quality/or economic reasons) ypu know which way to go.I do add buffers for pH and kh 1 or 2 times a week,and calcium every week or two on my 75 as test dictate but my 29 does not require same(both fairly evenly stocked?).http://www.aquariumforum.com/f18/water-changes-39477.html this is link to salt thread/also had fresh


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## susankat (Nov 15, 2008)

Hi Sully; there is no dumb questions but there can be dumb answers. Coralbandit has never given a dumb answer so you can go by what he says.


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## phys (Feb 4, 2011)

As I have seen in the past with just my tanks, a water change is necessary. Not only does it rejuvenate the minerals in it, it helps to get out everything nasty in the tank from fish food, fish poo, and coral secretions and poisons. 

When you do your water change, you look at your total water volume, not your tank volume. If you have a 20 gallon tank and you have a displacement of 5 gallons due to rock and sand, you should do your calculations based off the 15 gallons.. This is extremely important if you do supplements, additives, or calcium/alk/mg replacements. A calculation for alk on 20 gallons will add potentially dangerous amounts of alk to at 15 gallon water volume depending on your current levels and how fast you add it.


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## Sully (Oct 31, 2012)

Keep the answers coming everyone. I love hearing peoples opinions.

CB- I had read that thread not long ago when lurking the forums before joining.

Phy- Great points about sups, additives, meds and the like.


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## Reefing Madness (Aug 12, 2011)

So, here is the deal on WC. If your water parameters are in check, why change it? Your water will tell yoiu when its time. If yoiu have a big enough Sump, this of course will also help, will lengthen your time inbetween a WC. Next, if you Carbon Dose, this will lengthen your time also. Eveyone basically doses something in the tank, so Dose Trace Elements also along with the ALK, MAG, CA, etc. You tests and Corals will let you know when there is a problem.


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