How to calculate % water change?

[KWB]

I am new to the saltwater scene and have been lurking/researching for quite a while now. One item I can not find a answer for is: When you go to figure how many gallons you need for a 20 % water change, Do you deduct the volume taken up by the live rock and sand or do you just calculate it by total capacity of your tank? Thanks in advance.

[mdavis735]

I don't know what everyone else does,but i have always just figured the total volume of the tank.

[Captain Jack]

It probably doesn't matter so much how you calculate what percent you are changing. Some people change 10-20% a week, some people change 5-10% a year. Unless you have problems like nitrates too high, I can't see it mattering whether your 20% is gross tank capacity or net water in tank. (hmm.. not sure if those terms are appropriate, but they make sense to me.)

For things that do matter like dosing medications or something, gallons of actual water would be important.

[ErikH]

I don't know what everyone else does,but i have always just figured the total volume of the tank.

I do the same. I have a 75 and a 29g for a sump. I usually do 15-20g per week. I am running a CA reactor as well, but I feel that my tank looks nicer when I change more often because of trace elements etc. I say in the beginning, overdo your water changes. If you are having any problems, overdo your water changes. As long as you do the changes properly and on schedule, which is a must, you can and will be successful.

[ErikH]

I don't know what everyone else does,but i have always just figured the total volume of the tank.

I do the same. I have a 75 and a 29g for a sump. I usually do 15-20g per week. I am running a CA reactor as well, but I feel that my tank looks nicer when I change more often because of trace elements etc. I say in the beginning, overdo your water changes. If you are having any problems, overdo your water changes. As long as you do the changes properly and on schedule, which is a must, you can and will be successful. Salt is cheap.

[prof]

20% of 72g is 14.4g. I would recommend starting with this number and then decide what is most convienent for you. If it is easiest for you to mix and change 10g than do a 10g water change, if 15g do 15g, if 20g do 20g, etc.

20% is just a good base number to start your calculations. The most important thing is to be consistent. Pick what will work best for you and then do it. Don't worry about the exact number.

[mdavis735]

i had a 55 gallon tank with no sump.i had 3 of the clear water containers that were 5 gallon.it was easy for me to just buy that 15 gallons of water and mix it in and 18 gallon tub.so i did 15 gallon water changes on my 55.i had a nitrate problem so i did it pretty often for awhile there.got the nitrate problem solved though.but that was the easiest and most convenient so i changed 15 gallons at a time.