Alk rise mystery

[Aquariumaddictuk]

Good morning
I'm hoping for some opinions regarding an inexplicable rise in alk @Randy Holmes-Farley

It's been sitting steadily at 8.4-8.8 throughout day according to hanna.
I've noticed in the last two days it has suddenly risen to 9.9-10.
Salt is NYOS pure(tested at 8.5dkh)
15% water change performed weekly.
Tank has been consuming 1dkh per day steadily.
SPS dominant Mixed reef(75% SPS)

Other parameters

Salinity 35ppt
Cal 465
Nitrate 4.6
Phos 0.03
Mag 1410ppm
Temp 25.5
RODI 0tds

I recently received my ICP test back which showed a deficiency in iron & iodine so have been dosing those to reefzlements dosing calculator.
Only other changes have been twice weekly dosing of DIY coral snow(97% purity calcium carbonate) again following recommended dose.
I dose a very prudent amount of seachem fuel(50% of recommended weekly dose)

I'm puzzled as to what could cause consumption to cease or all to rise but perhaps the above will give some clues.

 

[Randy Holmes-Farley]

Most likely causes are, IMO:

1. Dosing pump issues not dosing the amount you think (is dosing automated?)
2. Test error in alk (how are you measuring it? reagent running low in autotitrator?)
3. Coral snow still in sample when testing alk (it can dissolve in the titration, giving a false high reading)
4. Something unknown irritating corals and reducing consumption
5. pH lower than usual reducing demand for alk

 

[Aquariumaddictuk]

Most likely causes are, IMO:

1. Dosing pump issues not dosing the amount you think (is dosing automated?)

I'll recalibrate dosing heads(reefdose 4 only 4 months old)

2. Test error in alk (how are you measuring it? reagent running low in autotitrator?)

Measuring with Hanna alk checker.new reagent just opened

3. Coral snow still in sample when testing alk (it can dissolve in the titration, giving a false high reading)

I deliberately didn't didn't dose any CC for day before the test

4. Something unknown irritating corals and reducing consumption

Certainly nothing visible. SPS PE still great.millie showing some filaments but never quite sure if that's a natural feeding response or stress signal.no visible issues with LPS

5. pH lower than usual reducing demand for alk

pH testing at the usual 8.1-8.3

 

[Randy Holmes-Farley]

Measuring with Hanna alk checker.new reagent just opened

That might be the "issue". with no real alk change, if the new reagent exactly corresponded to the sudden "rise".

 

[Aquariumaddictuk]

That might be the "issue". with no real alk change, if the new reagent exactly corresponded to the sudden "rise".

I hadn't considered that.certainly a logical possibility.having just retested with same(new) reagent-its showing an alk drop of .2dkh which is still illogical given the usual consumption over the specific timeframe.
Baffling.
I'll pick up a new salifert kit tomorrow & see how/if that collates & monitor closely over next few days without dosing.
Many thanks for the replies @Randy Holmes-Farley