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Alkalinity rising without dosing... possible causes?

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rynosreef

rynosreef

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Well, I will say that removing the sand bed is a maaajor destabilizing event. There's an enormous amount of nitrification going on in the sandbed, microfauna populations etc. When you take that out, the system will need to rebalance itself. During this time I wouldn't be surprised if calcification slows or stops until the system has regained equilibrium. So not having your alk rise now is a win in my book. In time, it should go back to normal if everything else is kept stable. How long has it been since you removed the sand? Also be sure your RODI filters aren't old. It can be easy to forget to change them and be letting in some pollutant.

In my case, and I'm sure most everyone's, keeping SPS happy is a moving target. My sps are absolutely doing better. During my ordeal and for a while after I had very little growth and a couple of my acros we're quite pale. So I really up'd my feeding and even starting dosing phosphate, as both my N and P were consistently undetectable. Now N and P are detectable and coloration has really improved, coralline is growing more rapidly etc. I suspect the sand/alk issue and the undetectable nutrient/pale SPS issue could be related in some way.

All that being said, I bought some frags a month or so ago and placed them on my frag rack to settle in and wait for signs of growth. They started growing, one even encrusting into the frag rack. So I figured it was a great time to place them on the rock. Wrong. They started to STN a few days later so are back on the rack to hopefully recover. So I'm now trying to figure that one out. Was it the rock? A pH spike from when we went out of town? Just stress from being handled? The phosphate dosing? I wish I knew hehe.
 

sgrosenb

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Cool - thanks for the feedback @rynosreef . Below are a few answers to your questions and a few questions I have:

How long has it been since you removed the sand?
It's been about 3 months

During my ordeal and for a while after I had very little growth and a couple of my acros we're quite pale
when you say a while after, about how long would you say that was? Like I said I'm going on 3 months and it's not looking too promising... My SPS haven't died yet, but I have multiple SPS who look like they might be on their way to dying...

In terms of nutrients, I haven't had an issue keeping NO3 and PO4 at detectable levels. If anything, my PO4 is too high at 0.15 or so (that's what my Hanna checker has it at... My Triton ICP shows it right at 0.03)
 

sgrosenb

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@Rp8 I think I've read that people with caribsea had the same problem too. I haven't seen a consistent trend with sand types. It strikes me that something else is going on in all of our tanks that is causing this, but I can't pinpoint it. I'm not positive, but I think it is personally tied to my issues with growing SPS
 

blasterman

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Curious what your typical tank pH is at and if you've tested dKH with another method.

A main reason we want to use carbonate based sand or crushed coral in our tanks is for this specific buffering capability.

C02 from fish or acids released during organic decomposition (or just low environmental CO2) slowly eats away the calcium carbonate substrate. The substrate doesn't just leech alk. This produces calcium and free carbonate like a slow burn calcium reactor. This is how some reef tanks sustain SPS without dosing, however the equilibrium dKH/pH/calcium is typically very low.
 

sgrosenb

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@blasterman interesting that you ask as I have a pretty rogue thread that goes into this as well here. Might be worth a read, despite the fact that it gets a bit hijacked and spicey at the end. In terms of checking dKH - I've kind of obsessed about it so I've tested with Neptune Trident, GHL KH Director, Hanna, LaMotte and Salifert. I'm confident that it's in line with what I'm seeing. In terms of pH - typically, it goes from 8.0-8.3 like clockwork, but when I open my windows or use a CO2 scrubber it can bump up a good bit higher than that.

You're the first person to touch on calcium - my calcium is high and it feels like it just keeps increasing on it's own as well. I've never mentioned that because high calcium doesn't seem to be detrimental, but it consistently tests at 500++ and I've never, ever added calcium to the tank in the ~2 years it's been running.

I'm curious if any of this gives you any pause or thought. Thanks so much.
 

sgrosenb

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I'll also add that I work from home and my wife stays home too, so we are home pretty much all day everyday; I've got to believe living in FL our CO2 is higher than the typical home, but my pH continues to be in a decent 8.0-8.3 range. Combine that with the fact that I have 3 kids and a dog, and everyone has been home for the past 6 months from COVID. But alas, my pH continues it's cycle of 8.0-8.3 daily. See below:
1596760352653.png
 

Randy Holmes-Farley

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@Rp8 I think I've read that people with caribsea had the same problem too. I haven't seen a consistent trend with sand types. It strikes me that something else is going on in all of our tanks that is causing this, but I can't pinpoint it. I'm not positive, but I think it is personally tied to my issues with growing SPS
Aragonite is aragonite. Brand should not matter and I cannot see any other type of sand boosting alkalinity unless it is made from cement or some other artificial material.
 

Randy Holmes-Farley

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You're the first person to touch on calcium - my calcium is high and it feels like it just keeps increasing on it's own as well. I've never mentioned that because high calcium doesn't seem to be detrimental, but it consistently tests at 500++ and I've never, ever added calcium to the tank in the ~2 years it's been running.

I'm curious if any of this gives you any pause or thought. Thanks so much.
I suggests that aragonite dissolution in sand is what you are seeing. Calcium necessarily rises when that happens,a bout 2.8 dKH to 18-20 ppm calcium rise.
 

sgrosenb

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I suggests that aragonite dissolution in sand is what you are seeing. Calcium necessarily rises when that happens,a bout 2.8 dKH to 18-20 ppm calcium rise.
Thanks @Randy Holmes-Farley it sounds like that is the culprit. I guess my next question is why? I'm don't understand the chemistry side of things very well, but I think in prior posts you mentioned it could be due to lower pH within the sand that breaks it down more quickly in some tanks than others. Could there be any other reason that the aragonite is dissolving quicker in some people's tank than others? Said differently - what would be causing that low pH within the sand itself? My tank has a pretty normal pH (see chart above), so I don't understand why mine and few other's tanks see this issue more than most.

There are likely thousands of tanks with aragonite sand, but only a few threads on here that discuss rising alk. I know some people with large coral loads would be able to mask the alk rise with their coral alk demand, but I would think a lot of newer tanks would have this issue; I just don't see many people having it. Thanks as always for your insight.
 
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Randy Holmes-Farley

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Thanks @Randy Holmes-Farley it sounds like that is the culprit. I guess my next question is why? I'm don't understand the chemistry side of things very well, but I think in prior posts you mentioned it could be due to lower pH within the sand that breaks it down more quickly in some tanks than others. Could there be any other reason that the aragonite is dissolving quicker in some people's tank than others? Said differently - what would be causing that low pH within the sand itself? My tank has a pretty normal pH (see chart above), so I don't understand why mine and few other's tanks see this issue more than most.

There are likely thousands of tanks with aragonite sand, but only a few threads on here that discuss rising alk. I know some people with large coral loads would be able to mask the alk rise with their coral alk demand, but I would think a lot of newer tanks would have this issue; I just don't see many people having it. Thanks as always for your insight.
pH is lower down in sand from organics degrading, producing CO2 with lowers pH. I've measured it myself and it is well below the bulk water pH.

The dissolution likely always happens to some extent (as I said, some great tanks monitored it over years and found the sand disappeared), but if your demand for alk and calcium is very low, this small addition exceeds your demand and alk may rise. Everyone else doesn't notice it as it is just making apparent demand very slightly lower than reality.
 

Randy Holmes-Farley

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This is one of the detailed chemical reactions that happens there to lower pH. I bolded the CO2 produced to make it more apparent:

Nitrate in the Reef Aquarium - REEFEDITION


Deep sand beds can develop low oxygen regions where nitrate is used by bacteria. They use it to metabolize organics that randomly diffuse into the sand from the water column. When the oxygen gets depleted in the sand, the bacteria can still oxidize the organics available by using nitrate instead of O2. In this situation, nitrate acts as an electron acceptor (e.g., an oxygen source) in place of oxygen (O2). The end result is that nitrate is converted into N2, and the N2 blows off of the tank to the atmosphere. The reactions that take place can be complex.22 In oxygen-containing environments, the reaction looks very similar to that shown above for plankton (ignoring phosphorus here):

organic + 175 O2 → 122 CO2 + 16 NO3– + 16 H+ + 138 H2O

where organic stands for a typical organic material ((CH2O)80(CH2)42(NH3)16) that is being metabolized. In the absence of O2, and taking the nitrogen species completely to N2 (which may happen in several reaction steps), we have the following overall reaction:

organic + 124 NO3– + 124 H+ → 122 CO2 + 70 N2 + 208 H2O

It can be seen that the process above produces alkalinity (by consuming H+). In fact, it is the exact same amount of alkalinity that was depleted when the nitrate was originally formed from foods, so the net effect of the nitrogen cycle on alkalinity is zeroed out.

In many aquaria, the process takes place to an extent sufficient by itself to keep nitrate at levels below 0.5 ppm. In others, it has not been adequate. Success may depend on the size of the bed, its composition (sand type, particle size distribution, depth, and life forms in it), and the demands put on it in terms of nitrate processing. It is rarely discussed by aquarists, but organics are critical for this process as well, and some aquaria may have more or less organic matter in the water (due to use of things like skimming or granular activated carbon) and this, in turn, can impact the nitrate conversion capability of a sand bed.

This process also happens in the pores of live rock, and in a variety of other environments in a reef aquarium.
 

Dan_P

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Aragonite is aragonite. Brand should not matter and I cannot see any other type of sand boosting alkalinity unless it is made from cement or some other artificial material.
Aragonite is aragonite? Consider this observation.

I recently had cause to examine new dry aragonite sand under the microscope. I stained it with methylene blue (this was an arbitrary choice, it was what I had at the time). Some, not all the sand grains picked up the stain. The pattern of the stain resembled “shadows“ of microorganisms I have seen on the sand grains in my aquarium. The only test performed on this sand so far was to see if these “shadows” would support oxygen consumption when inoculated with aquarium water.

Aquarium water by itself does not have much of an oxygen demand because there is little digestible nutrient content in the water. A typical BOD5 is tenths of a ppm of oxygen. When new dry aragonite sand was added to aquarium water, a significantly higher BOD5 was observed and in proportion to the amount of sand present.

This was only a screening experiment to determine if it was worth pursuing the investigation. This study is on my list of rabbit holes to explore :) So take it as a one off observation right now, and maybe, shoot me some questions that you might have about organic matter content of new aragonite sand.
 

Randy Holmes-Farley

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Aragonite is aragonite? Consider this observation.

I recently had cause to examine new dry aragonite sand under the microscope. I stained it with methylene blue (this was an arbitrary choice, it was what I had at the time). Some, not all the sand grains picked up the stain. The pattern of the stain resembled “shadows“ of microorganisms I have seen on the sand grains in my aquarium. The only test performed on this sand so far was to see if these “shadows” would support oxygen consumption when inoculated with aquarium water.

Aquarium water by itself does not have much of an oxygen demand because there is little digestible nutrient content in the water. A typical BOD5 is tenths of a ppm of oxygen. When new dry aragonite sand was added to aquarium water, a significantly higher BOD5 was observed and in proportion to the amount of sand present.

This was only a screening experiment to determine if it was worth pursuing the investigation. This study is on my list of rabbit holes to explore :) So take it as a one off observation right now, and maybe, shoot me some questions that you might have about organic matter content of new aragonite sand.
Where did you get that batch of sand?
 
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