Red sea Coral pro and Alkalinity

[Thor2j]

I don't understand something about RSCP. I have 2 tanks I use it in. A reefer 170 and a reefer 525. This is the only salt I've used since day 1. When I mix the salt I've tested it around 12dkh.
So I do a routine 10% water change weekly on both tanks. I'm currently not dosing on my 170 and it spikes DkH initially a little but always settles a couple days later at 6.7. I use 3 seperate tests including a hanna and always get same on all 3. The reefer 170 has 4 zoas, a couple small acans, and a couple trumpets.

My 525xl has quite a few frags so I end up dosing about 25ml oceans blend to keep it steady at 8.7. Occasionally I'll do a 25% water change, turn the dosing off the day b4 I do it and later that day it's only around 9. Next day right down to 8.7.

To me the math doesn't make sense. 25% h2o change and really only going from 8.5 to 9 basically.

On the 170 really doesn't make sense. DkH falls like a rock after water change initial spike.

Does RSCP "loose" it's DkH that fast??

I really don't mind it as I have a methodology to my changes especially on my 525. Was thinking about changing to a salt more in line with my DkH I want to run (around 8.5).

 

[Randy Holmes-Farley Verified Community Expert]

A 25% change of water using 12 dKH water in a tank at 8 dKH will boost alk to 9 dKH.

Shutting off the dosing will partly offset that, and demand for alk rises as alk rises, which means it drops back faster.

 

[Thor2j]

A 25% change of water using 12 dKH water in a tank at 8 dKH will boost alk to 9 dKH.

Shutting off the dosing will partly offset that, and demand for alk rises as alk rises, which means it drops back faster.

Hi Randy,

I realize it's chemistry and math but for whatever reason it doesn't add up. I start around 8.5 and end up 9.1 after water change.

 

[Thor2j]

Plus this doesn't address the rapid loss of DkH in my other tank

 

[Randy Holmes-Farley Verified Community Expert]

Hi Randy,

I realize it's chemistry and math but for whatever reason it doesn't add up. I start around 8.5 and end up 9.1 after water change.

Well, it is measurement error of some sort, either tank volume, change volume, or the alk measurements. It's not off by that much, 0.6 dKH vs 1.0 dKH. Since it involves two alk measurements and the volume estimates, that's not unreasonable.