Water change quantity calculation

[krash7172]

So how exactly is the water change amount calculated? Total volume of water? I realize necessary wcs will vary with stocking but when I hear a % I'm not sure. I have a large sump. I assume tank gallons minus rock and sand volume plus how much water is in sump?

I have a 180 tank with about 40 gallons of sand and rock. My sump holds about 60 gallons. I can do a 30 gallon WC without removing any water from the tank and that equates to 15% of total water in my system. I planned to do this twice per month. After 6mo, nitrates are still very low so I'm not worried, just curious how the calculation is done.

 

[Ranjib]

I dont know the theory behind it, but I was recommended by local reef club member and in online forums that 10-15% weekly is a very good schedule, so I stick to it. I know there are folks who does it lot less.. there are methods (like triton) which does not recommend water changing at all (unless param are skewed), I have seen a video from reef builders, covering Dr. Joshi's tank, and i remember he also mentioning that he does not change any water.

I'll say depending upon how much you feed, what all filtration you have , and what live stock you are planning to keep , you can dial the numbers.. but to start with probably 10% weekly is not a bad number (by volume)

 

[Forsaken77]

So how exactly is the water change amount calculated? Total volume of water? I realize necessary wcs will vary with stocking but when I hear a % I'm not sure. I have a large sump. I assume tank gallons minus rock and sand volume plus how much water is in sump?

I have a 180 tank with about 40 gallons of sand and rock. My sump holds about 60 gallons. I can do a 30 gallon WC without removing any water from the tank and that equates to 15% of total water in my system. I planned to do this twice per month. After 6mo, nitrates are still very low so I'm not worried, just curious how the calculation is done.

In the beginning it's best to do 10% of the tank-only volume per week. After the tank gets established more than it could be 20% biweekly and maybe monthly, depending on the stocking levels. But 10% per week in the beginning is a good reference point.

 

[krash7172]

My question is what do you base the calculation on? Sorry, I'm an engineer :)

 

[krash7172]

Add sump volume or not? Subtract the rock and sand?

 

[reeferfoxx]

It's based on water volume not tank size. You would calculate the amount of gallons in the DT plus the estimated gallons of the sump.

 

[TonapahNorth]

Again, it’s more of an anecdotal rule of thumb, than anything scientific I’m aware of anyway. Routine water changes are based on total system actual water volume.

Here is a nice article by @Randy Holmes-Farley that was helpful in my understanding of waterchanges - how much and how often.

http://reefkeeping.com/issues/2005-10/rhf/index.php#4

It answers your question as well - it’s bssed on actual system water volume.