Alkalinity increase without dosing

[griff500]

The KH Director has been checked against a test kit from time to time and always matches.

The tank is running fallow and I am dosing N and P and a tiny bit of food from time to time.

Alkalinity was stead and corals were doing well but it increased (from 7 to 7.6), then down, then up... Corals are struggling (colours are going pale). I would associate paleness with a lack of nutrients in my tank (I've tested with a PAR meter and it was in a range I am perfectly happy with and I had good growth and colour), but I try to increase N without ever getting it above 1 and P varies between 0.04 and 0.08.

Numbers have also been verified with ICP.

Any ideas how on earth Alkalinity can increase when I'm not dosing it? I understand that corals not doing well would mean reduced Alkalinity uptake and thus a higher reading IF I continued dosing but the moment it started rising I stopped dosing and yet it has still gone up (then down and then up).

I've increase N to try and get that higher but would appreciate any ideas about this.

Perhaps some amino acids or something to increase N and provide food?

 

[homer1475]

Your dosing nitrates, but what exactly are you doing?

Also what test kit(s) are you using? 7 to 7.6 is well within some test kits margin of error(0.5DKH). Don't get hung up on a number and try to maintain that number. It's nearly impossible with our hobby grade test kits. Instead try to maintain a range, say something between 7 and 7.5 is perfectly acceptable.

 

[griff500]

The readings are from a KH Director - verified with a test kit as I was surprised for Alkalinity to rise when not dosing. I believe the KHD has a lower margin of error than 0.5 and I've had very consistent results from it, moving around no more than 0.1 until recently, so this is a change.

Dosing Nitrates using ATI Nutrition CNP.

 

[Erasmus Crowley]

...Dosing Nitrates using ATI Nutrition CNP.

See this post: https://www.reef2reef.com/threads/alkalinity-rising.269520/#post-3228821

Bacteria use carbonate alk to turn ammonia into nitrate. When that nitrate is consumed, either by becoming biomass or nitrogen gas, that original alkalinity gets returned to the water.

If you are dosing nitrates, and something is consuming them, then you are effectively dosing alk.