Alkalinity won't decrease

[Jason Scalise]

Hello,
I am currently puzzled about my alkalinity water chemistry. It will not seem to decrease and if anything...is creeping up.
I have read previous threads about this topic but did not seem to get the insight I felt I needed but it did seem to be a bit confusing for everyone too.
Here is the background.

• 115g tank. (Red Sea Reefer 425XL)
• 1+ year old.
• minimal corals right now. just 3 SPS frags.
• (I battled a major dino outbreak about 3 months ago which devastated my frags (the treatment) that I had at the time. I did not fully appreciate too low nutrient levels....I do NOW. I have seemingly won that war for now and things seem to be in relative balance).
• Prior to World War 3 on the dino's, my Alkalinity hovered around 7.8 dKh but was not super stable. I was dosing with ESV 2 part to keep up. about 15mls per day seemed to do the trick.
• In the new Dino-free era, because I noticed my Alk going up, I stopped dosing alk and calcium to re-measure and recalibrate the daily consumption.
• I stopped dosing Alk and Calcium 2 part several weeks ago and yet it kept creeping up and now sits at 9.0
• Therefore, my alkalinity has increased to 9.0 dKh "on its own". Calcium staying around 450ppm.
• Coraline is growing and the 3 SPS frags I look very healthy. Good PE.

Parameters
Assessed daily at the same time each morning
Alk 9.0 dKh (hanna)
Calcium 450 ppm (hanna)
Phos .1ppm (I dose daily with NeoPhos to keep it there) (hanna)
Nitrate >4 ppm (red sea)
salinity 1.026 specific gravity (very stable)
Temp 79 deg
salt mix Tropic Marine Pro

Alkalinity of new salt water is 6.8 dKh (65g reservoir and I use a dosing pump to do about 0.5% change per day)
Fresh water top off is RO/DI clean.
Rock is Caribsea LifeRock dry live rock. Again this has been in the tank for over a year.
Sand is Caribsea aragonite
About 5 fish. I feed as heavy as seems reasonable to keep the Phosphate up but the fish only can eat so much.
Lots and lots of pods.


So my question is: With no additives, no dosing, etc...how the heck is the Alk going up?
Clearly it is coming from somewhere from a water chemistry standpoint.
Perhaps the rock? ok...but after a year? it is not manmade concrete stuff. so how could that be?
did I overdose the Alk in the preceding months and now it is "leeching" out of the environment? That does not sound like a "thing" in the way phosphate or calcium could be leeching out of the tank 'environment'.

I will say a dKh of 9.0 is not in itself a problem per se....but not being able to understand the rise from 7.8 to 9.0 "on its own" is in my mind.
I feel I am missing something from my biochemistry days. I can't make the connection other than to say....it must be coming from somewhere to be increasing.

Any insights or feedback would be welcomed.
thanks!!
jason

 

[KrisReef]

Could your 2 part from past dosing have precipitated on the substrate and now it is leaching out to raise dKh?

 

[Jason Scalise]

I don't know if that is a "thing". ...hence my post/question.
If so, then perhaps yes.
thoughts?

 

[KrisReef]

I don't know if that is a "thing". ...hence my post/question.
If so, then perhaps yes.
thoughts?

It is the only thing that makes sense to me, but I will be curious to see what others think especially if there is an alternative hypothesis to your observation/question. Ion exchange and equilibrium are complicated solutions, and seawater is a very complicated solution because of this. So, yes, I think it is leeching. The other variable that jumps out as I think further is the test method you are using. I have no reason to doubt your results but perhaps the test kits are old? I have gotten test errors from aging kits in the past for dKh.

 

[proxy001]

what does your TDS read on the RODI?

 

[Perthegallon]

I had the same issue and i never even two part dosed my theory it was coming off the dry rock I used but really never figure it out

 

[homer1475]

is your sandbed hard?

While I never had a raise in alk, early on in my reefing career I didn't understand dosing, and as such I way overdosed ALK. Which in turn turned my sandbed to complete rock.

This was my sandbed when I removed it:

 

[Jason Scalise]

Thank you all.
answers to your questions:

testing kit: Thought of that. Yes. So, switched to band new reagents...with same results.

TDS on RODI = zero. I am particular about that.

Substrate. YES! Although not as “bad” as your picture, yes, I have some of that in my sand. Sand turning into “stone” clumps. I would say perhaps 10% is like that.
Yes, I too likely overdosed my 2 part over the last year during my learning curve.

so perhaps I have a calcium carbonate storage unit in my substrate that is now buffering and leeching Alk back Into the water column? Coincidentally, I left my Wav pumps on higher power for longer than normal yesterday causing a bit of a sand storm and bare bottom area. I noticed a Alk spike this morning.Perhaps not related....

If a build up in the substrate is my issue, here is what I am thinking:
Leave it be but monitor it for now...as opposed to removing/replacing substrate. As corals grow and use it up, follow the decrease and dose accordingly as needed.

How long you you expect it leech back? I know it depends on how much is there. But what is the capacity to do so? A month? Several months?

thanks!

 

[rmurken]

What’s your pH typically? Sounds like it would be on the high side. I don’t think aragonite sand and rock will net add to your alkalinity unless you’re using a calcium reactor ... I.e., mixing it with something like vinegar that will get converted to alkalinity.

I will say that I have had, and continue to have, a day or a week here and there where my Alk stops falling or even bumps up a little. I have never found a satisfying explanation, but my tank seems to be fine.

It sounds like your tank is fine too, and I bet you’ll find that your Alk consumption starts back up again as mysteriously as it stopped. Weird phenomena like this are part of the hobby.

And now you know what too much two-part can do!

 

[rmurken]

Oh other datapoint: my tank is low-demand, and it sounds like yours is too. About .5 dKH or so/day when it’s humming.

Also, if you want to go a little deeper, read Randy’s articles on Ca/Alk, where he goes into some of the stuff that can contribute to alkalinity, like denitrification, vinegar dosing, etc. May not be the answer, but more knowledge...part of the hobby.

 

[Jason Scalise]

Thank you.
Yes, I have read those articles about by Randy regarding denitrification. I thought I was on to something there in my case given my chemical warfare on the dino's but suffice it to say it did not match too well my situation from what I could tell.
N03 has not been rising/falling. Not so say it is not contributing to my "issue"...but did not seem to be the magic bullet.

pH is oscillates between 8.15 and 8.30 in a normal diurnal pattern...over the last 6 months. stable.

I do not have a Ca reactor.

 

[rmurken]

This sounds like an issue I have occasionally. I have not seen a good answer to it, but it also has not caused a problem for me. I just stop dosing for a bit and it eventually gets back to normal.