Alk / water change question

[Maho.B]

Hello. I'm scheduled to do a 15% water change on my reef tank today. My current alkalinity is 8.2

My water change water alkalinity is 7.3 which mixed up a little lower than usual as it's normally around 7.8 or so.

Will adding 7.2 water to my 8.2 reef be too much of a swing? I have mostly sps so just wondering if it's risky. Thank you.

 

[allof fish]

How big is your tank? Shouldn’t be a problem at all. It will just mix right in with the rest of water. Might barely move but not much. I keep my tank at 8.3-8.6 and use tmp which mixes to 7 and I haven’t really noticed a difference at all after

 

[Maho.B]

Ok good to know. The total volume of water in my tank is 110 gallons. Thank you

 

[X-37B]

I prefer to match alk. Use your alk 2 part, I use esv, and just bring up the alk. Simple and easy to do.

 

[ShakeyGizzard]

All salt mixes are different, I prefer a 9.3 to 10.0 dKH, that's why I use Instant Ocean Reef Crystals. It mixes up at 10.5 to 11.0 dKH. Makes maintaining the dKH easier. 8 to 12 dKH is prefered.

 

[Randy Holmes-Farley Verified Community Expert]

It will be fine.

That change will drop alk from 8.2 dKH to 8.07 dKH. A trivial drop.

 

[Maho.B]

It will be fine.

That change will drop alk from 8.2 dKH to 8.07 dKH. A trivial drop.

Whoa! That's all the effect it will have... thanks for that info.

 

[Garf]

Whoa! That's all the effect it will have... thanks for that info.

I would double check your make up salinity though, to rule out a mixing error.

 

[Randy Holmes-Farley Verified Community Expert]

Whoa! That's all the effect it will have... thanks for that info.

You’re welcome.

Alk (or most things we measure except pH) are just the weighted average of the two solutions.

0.15 x 7.3 dKH + 0.85 x 8.2 dKH = 8.07 :)