NSW - Alk dropping

[calli]

Hey everyone,

Since I purchased this box of Fritz blue box I have noticed the Alkalinity dropping overnight. I had read that someone else had noticed this with their salt as well.

At first I was mixing the salt right into the cold RO/DI water and putting approximately what it would take for 5 gallons at 35ppt. I always had tested the first new batch from a new box and this usually right about an hour or two after mixing.

8.4Dkh
410 Ca
1395 Mg

Then I had read that someone had seen the alk dropping overnight. So, I tested in the morning and sure enough, the alk was at 7.2Dkh or so. Once this happened I decided to mix the salt just as it says on the box.

Heat water to 70 degrees then slowly add the salt. I noticed that the mix was clearer and not as much precipitate as there was the first method of mixing, however, the alk then dropped to 7.4Dkh overnight.

Communication with Fritz:

At this point I emailed Fritz for my testing results on the batch and everything looked fine. All my original numbers were in the range.

Email to Fritz Support:
I am having an issue with the box of salt that I have currently with the Alk dropping overnight.

I raise the temp of the RO/DI water to 70-75 degrees, then I begin to add the salt very slowly, over about 5-6 hours. I test the fresh batch about 1 hour after mixing to 35ppt and I am at 8.4 Dkh.

I then test again in the morning at I am at 7.4Dkh

Can you tell me if this is normal?

FRITZ REPLY:
Are you mixing and/or aerating the saltwater overnight? Once the dry salt has dissolved fully we recommend discontinuing mixing if storing for longer than a few hours. Excess circulation can cause the alkalinity to drop.

I do leave the Mj1200 running in the bucket overnight with the salt, as the pump keeps the temp around 70-80 degrees.

Can someone please explain the scientific process around why this would be true? or is Fritz just blowing me off?

Thank you,

 

[Randy Holmes-Farley Verified Community Expert]

Alk can drop in salt mixes, especially when they are first mixed or when they are warm by formation of precipitated calcium carbonate. that is why Red Sea recommended little heating or mixing or storing of Coral Pro salt mix.

Also, when you first mix it, there may already be some calcium carbonate that formed in the bucket, or maybe soon after mixing, but it can stay suspend as fine particles for a while, and if those particles get into an alk test, they will dissolve and give a false high reading for the alkalinity. When they settle out the values drop, even if the actual alkalinity has been unchanged.

This has more:

What is that Precipitate in My Reef Aquarium? by Randy Holmes-Farley - Reefkeeping.com

Figure 1. The residue on the bottom of the plastic trash can that I use to mix Instant Ocean. I rarely clean it out. The solid is most likely calcium carbonate.

 

[calli]

Alk can drop in salt mixes, especially when they are first mixed or when they are warm by formation of precipitated calcium carbonate. that is why Red Sea recommended little heating or mixing or storing of Coral Pro salt mix.

Also, when you first mix it, there may already be some calcium carbonate that formed in the bucket, or maybe soon after mixing, but it can stay suspend as fine particles for a while, and if those particles get into an alk test, they will dissolve and give a false high reading for the alkalinity. When they settle out the values drop, even if the actual alkalinity has been unchanged.

This has more:

What is that Precipitate in My Reef Aquarium? by Randy Holmes-Farley - Reefkeeping.com

Figure 1. The residue on the bottom of the plastic trash can that I use to mix Instant Ocean. I rarely clean it out. The solid is most likely calcium carbonate.

Thank you Randy.
So best process would be to mix as they say on the box until clear then stop the pump and seal the bucket for a waterchange next day or next day after that?

 

[Randy Holmes-Farley Verified Community Expert]

Thank you Randy.
So best process would be to mix as they say on the box until clear then stop the pump and seal the bucket for a waterchange next day or next day after that?

If the exact alk is important to you, start with unheated water, and add salt slowly with vigorous mixing until is in essentially clear. Then if you need to, heat with some continued stirring to the required temp, and use it.

Air exchange is not the big concern, but mixing in a room with elevated CO2 will reduce any precipitation.

You could strongly reduce precipitate and lower pH if you add a little soda water to the water before any salt.