25% water change with new salt

[Pardsie]

Is there a formula for determining how much alk will change by switching from one salt brand to another. Have been using Aqua forest and am currently changing to IO reef crystals which has much higher alk. Doing 25% water change on a 210 gallon reef every 2 weeks.

 

[ludnix]

Disregarding coral consumption I believe the formula would be (current tank dKH - IOReef Crystals dKH) * 0.25 = anticipated increase in dKH.
There may be other factors involved depending on whats in the salt so your milage may vary.

 

[Randy Holmes-Farley Verified Community Expert]

[emoji106]. Another way to think of it is: 0.75 x current alk + 0.25 x new water alk.

 

[Randy Holmes-Farley Verified Community Expert]

There should be no other factors.

 

[Pardsie]

Thank you both

 

[Pardsie]

Thank you both

Does that mean my alk will continue to rise if I continue using reef crystal salt for water changes? Considering the last change resulted in alk dkh 9.

 

[Skydvr]

It depends on what your reference point is.

If no alkalinity was consumed, then yes, it would slowly creep up at a diminishing rate until it eventually matched the new water (it would take an infinite ammount of water changes to actually reach equalibrium (technically you would never actually reach equilibrium, but we can’t measure that low. Semantics, sorry)). You would fairly quickly hit a point where you couldn’t measure the difference between the tank water and new water.

If you are not dosing alkalinity and let it drop during the week, the water change will bring it back up higher than it would have with IO. Depending on how much is consumed, you may see larger swings between water changes. Without some alkalinity additions or periodic large water changes, you will see your alkalinity slowly decrease over time if waterchanges aren’t able to keep up with the alkalinity uptake.