alk drops after water changes

[CindyKz]

I have a 75 gal mixed reef (30 gal sump) that I do a 10 gal water change on every 2 weeks (ish). I've noticed that my alk consistently drops the day after the water changes. Between changes it stays 8.2-8.5, but after changes it drops to 7.7 or so. I test my fresh saltwater before my change and it is usually around 9.0, Fritz salt. This time it dropped from 8.7 (I was a little high for some reason) to 7.7.

If my saltwater is testing approximately where I want it, how do I prevent this? I don't see any new precipitate.

TIA

Cindy

 

[Robink]

this is something for @Randy Holmes-Farley .

 

[norfolkgarden]

I have a 75 gal mixed reef (30 gal sump) that I do a 10 gal water change on every 2 weeks (ish). I've noticed that my alk consistently drops the day after the water changes. Between changes it stays 8.2-8.5, but after changes it drops to 7.7 or so. I test my fresh saltwater before my change and it is usually around 9.0, Fritz salt. This time it dropped from 8.7 (I was a little high for some reason) to 7.7.

If my saltwater is testing approximately where I want it, how do I prevent this? I don't see any new precipitate.

TIA

Cindy

Bump

 

[WWIII]

How long do you let it mix before you do the waterchange? Do you test the new mixed saltwater right before you do the waterchange?

 

[Jwheld]

Is your water at the same salinity and temperature? I believe they both influence tested alkalinity.

 

[Makomek]

I have that happen when I used Fritz salt . I keep my Alk at around 8dkh and the new salt mix is 8.5dkh at 1.025 but after the 10-15% WC for couple hours my tank Alk is at 7.0-7.5. I don't know why it happen but after switching to regular IO I don't have the drop anymore.

 

[CindyKz]

How long do you let it mix before you do the waterchange? Do you test the new mixed saltwater right before you do the waterchange?

2 hours max, and yes

Is your water at the same salinity and temperature? I believe they both influence tested alkalinity.

Yes to both

I have that happen when I used Fritz salt . I keep my Alk at around 8dkh and the new salt mix is 8.5dkh at 1.025 but after the 10-15% WC for couple hours my tank Alk is at 7.0-7.5. I don't know why it happen but after switching to regular IO I don't have the drop anymore.

So your alk stays low for a couple of hours, then returns to normal? Or drops a couple of hours after the water change?

I've never tested immediately following a water change. I have a box of Kent that I won in a raffle - I think I am going to switch to that for a while and see what happens. Although it would suck if I need to switch, I have 3 boxes of Fritz in the basement :(

 

[chipmunkofdoom2]

What test kit are you using to test alkalinity?

 

[Makomek]

So your alk stays low for a couple of hours, then returns to normal? Or drops a couple of hours after the water change?

I've never tested immediately following a water change. I have a box of Kent that I won in a raffle - I think I am going to switch to that for a while and see what happens. Although it would suck if I need to switch, I have 3 boxes of Fritz in the basement :(

My Alk stay low until I dose soda ash to bring it up. I have seen others have low alk with fresh mix Fritz salt after 24hr of mixing around 7dkh. Bad batch maybe? Try test the Alk on a new mix Fritz salt after 24HR of mixing and see whats the number.