What could be causing my alkalinity to rise in a system with no dosing?

[zoaprince]

The only things I dose are Phosphate and Nitrate.

My alkalinity was conisistanly 8.0-8.3 for almost 2 years, so I didn't test for a month. All my hammers looked terrible 2 weeks ago so I tested and my alkalinty was 10.3 (salifert). I've done 2 %25 water changes since then and my alk is now at 9.3. I haven't determined if it's still going up but what could have caused it to go up? A couple of guesses.

• Crushed coral substrate deteriorating
  

  • It's been almost 2 years with this substrate​
• Coralline algae dying off
  • Maybe from the fluctuating alk, but I've noticed coralline dying off and I've seen it just flake off when hitting it with a turkey baster.

Any other reasons?

My current params

Alk - 9.3 (salifert)
Mag - 1350 (salifert)
Calcium - 430 (salifert)
Phosphate - .05 (hanna)
Nitrate - ~8 (nyos)

^These were taken just now with the lights off (if that matters).
Thanks!

 

[blaxsun]

Maybe a bad batch of salt?

 

[arking_mark]

What size tank? Do you do water changes? If so what salt?

Also, I believe dosing Nitrate will increase alk as it gets consumed.

 

[zoaprince]

What size tank? Do you do water changes? If so what salt?

Also, I believe dosing Nitrate will increase alk as it gets consumed.

20 gallons. 5 gallon water change every week with Fritz blue box.

I do recall reading that alk rises when nitrate goes down. I wonder if it could have gone up 2 units because of it?

 

[Randy Holmes-Farley]

Dosing nitrate adds alkalinity.

http://reefkeeping.com/issues/2004-12/rhf/index.htm

For each 50 ppm of nitrate that is consumed, 4.5 dKH of alk is added:

Likewise, equation 3 (below) shows the uptake of nitrate and CO2 into macroalgae to form typical organic molecules:

122 CO2 + 122 H2O + 16 NO3- --> C106H260O106N16 + 138 O2 + 16 HCO3-

Again, one bicarbonate ion is produced for each nitrate ion consumed.

 

[arking_mark]

Fritz blue box parameters: Salinity 35 ppt [1.0264 sg] Calcium 400-450 ppm Magnesium 1350-1450 ppm Alkalinity 8.0 - 9.0 dKH Strontium 9 ppm Potassium 400 ppm

So if salt batch closer to 9dKH...that could also contribute.

 

[zoaprince]

Dosing nitrate adds alkalinity.

http://reefkeeping.com/issues/2004-12/rhf/index.htm

For each 50 ppm of nitrate that is consumed, 4.5 dKH of alk is added:

Likewise, equation 3 (below) shows the uptake of nitrate and CO2 into macroalgae to form typical organic molecules:

122 CO2 + 122 H2O + 16 NO3- --> C106H260O106N16 + 138 O2 + 16 HCO3-

Again, one bicarbonate ion is produced for each nitrate ion consumed.

Thank you Randy! That definitely raised it then. It's interestting how I've been dosing over a year and only recently saw the uptik.

To be clear, crushed coral and dying coralline would not have caused it?

 

[Randy Holmes-Farley]

Thank you Randy! That definitely raised it then. It's interestting how I've been dosing over a year and only recently saw the uptik.

To be clear, crushed coral and dying coralline would not have caused it?

Slow dissolution of sand and crushed coral can also add alkalinity (and calcium, but you aren't likely to notice the calcium).