Alkalinity not changing over 14 day period??

[RyanSweet]

A little back story - 75gal mixed reef (mostly LPS), 30gal sump/refugium, Reef Octopus 150int skimmer, 2 Jebao pp20 powerheads, sb reef 48" leds. Tank has been up and running for over 8yrs with no major changes (or crashes) in over 3yrs. I have a spectrapure 5 stage RODI that is reading 0 TDS on the output of a dual meter, and that's what I do my water changes and top off with. Using Fritz salt.

I had some issues with stability and algae a little more than 3yrs ago so I made a few big adjustments and started actually monitoring things on a more consistent basis. Over the past 2yrs I've had great growth and color on all of my LPS coral (I'm a big meat, trachy, plate fan), a large zoa garden (nothing with fancy names, just ones I like the color), and the few SPS I have (Oregon tort, sunset mille, green slimer, pink lemonade). I noticed at the beginning of the year (first week of January) that my SPS polyp extension wasn't as pronounced as the ~1 1/2yrs previous and growth had pretty well stopped. No RTN/STN or anything of the likes that I've seen so far. I just figured there may be a lull in things as there is variance with this hobby. I normally test 1 time a month (1st Sunday, before and after a 20gal water change) but had started testing more frequently after noticing the change in PE and growth.
I had been dosing Randy's 2 part alk/ca but noticed that my alk was a little higher than I like (~10dKH on Salifert test) on January 14, 2018. I did a water change and tested again to with the same results so I stopped dosing alk and calcium.
Here are my overall test results as of Sunday, February 11(All tests done with Salifert kits, bought on January 14, 2018. Except po4 - which was Hanna ulr, temp - digital display, and salinity - portable refractometer from Premium Aquatics calibrated with 1.026 fluid):

Temp - 77.8
Salinity - 34ppt
Alk - ~9.0dKH
Ca - ~410
Mag - ~1380
NO3 - ~3ppm
PO4 - ~0.7ppm

These are what I test as I feel they are the most "important" for my tank setup. All of the levels are within minimal fluctuations of what has been tested over the last 2yrs, except alk hasn't changed at all since January 28, 2018. I haven't been dosing alk since January 14 and had tested it specifically every day at 7:00pm from January 28 to February 11, 2018.

Does this seem strange? Do you guys have any advice that could point me in the right direction if there's something I should check?

Thanks in advance for any help!

 

[Ocelaris]

I'd retest with another kit. It sounds like you've already discovered the wonders of Hanna for phosphorus, I'd suggest their alkalinity test kit. Calcium is a little low though? If your nutrient input and output match to keep those parameters stable like you say, you should be exploding with growth (short of the calcium level which is within error range). My nitrogen and phosphorus fluctuate quite a bit, and there is a significant lag if I let them get too low before the corals show good pe again.

 

[RyanSweet]

I'd retest with another kit. It sounds like you've already discovered the wonders of Hanna for phosphorus, I'd suggest their alkalinity test kit. Calcium is a little low though? If your nutrient input and output match to keep those parameters stable like you say, you should be exploding with growth (short of the calcium level which is within error range). My nitrogen and phosphorus fluctuate quite a bit, and there is a significant lag if I let them get too low before the corals show good pe again.

I should have mentioned, the new test kit was purchased due to an older kit giving me the same readings, and I took a sample to my LFS and had them test as well. Their salifert test read the same and he tested with an API with a slightly lower result. My N's and P's will fluctuate a little but have been pretty stable for the last 1 1/2yrs or so and I've seen great growth up until this.

 

[RyanSweet]

I bought another Salifert alkalinity test kit and am getting the same (~9.0dKH) reading after not dosing any alk. I just don't see how this is a possibility. Any "experts" have advice for me to try, or point me in another direction?

 

[Randy Holmes-Farley Verified Community Expert]

Did you do any water changes during this period?

What else, if anything as you adding to the tank?

 

[RyanSweet]

Within the 2 week time frame that I've been testing I have not done water changes. I have only dosed calcium throughout this period as well (normally dose alk, ca, mag when needed). I feed heavy and do monthly water changes of 20gals, total water volume ~85gals.

 

[Jeremy Luke]

I'll be interested to see what kind of responses you get. My current tank has only been running about 11 months. Corals went in about 9 months ago. I had some small daily consumption for a few months. I then noticed my Alk climbing. I now only do water changes (stopped dosing entirely) with low Alk salt and my Alk stays at 9. Most pieces aren't really growing. I've got good PE on most. A couple of pieces are growing well.

 

[Randy Holmes-Farley Verified Community Expert]

Within the 2 week time frame that I've been testing I have not done water changes. I have only dosed calcium throughout this period as well (normally dose alk, ca, mag when needed). I feed heavy and do monthly water changes of 20gals, total water volume ~85gals.

Pure calcium chloride? Some calcium products (e.g., Seachem Reef Calcium) boost alkalinity too, even if they do not say it on the label.

 

[Randy Holmes-Farley Verified Community Expert]

FWIW, if nitrate is declining through consumption or denitrification, that also boost alkalinity.

 

[RyanSweet]

FWIW, if nitrate is declining through consumption or denitrification, that also boost alkalinity.

I am using food grade cacl2 (not ice melt), can't remember the brand but can tell you when I get home this evening. I definitely didn't know about denitrification causing an increase in alkalinity, I'll look more into that. Thank you for the reply(s).