Calcium dropping much faster than alkalinity when using kalkwasser

[Adam Obenauf]

So this is a weird question for you guys (particularly Randy). When I use kalkwasser my calcium drops much faster than my alk. For example I just checked and I'm reading 8 dKH and 370 ppm Ca after a week of using kalk in my topoff water. It was 8.4 dKH 430 ppm Ca at the beginning of the week. I brought the Ca up to 420 ppm but by next week it will be back to the same. I have confirmed the readings in Salifert, Red Sea, and API test kits. The corals also stop growing when the Ca drops so I know it is in fact really happening. I do not have this issue when using balanced two part dosing even for months at a time. Only when using Kalk. I have tried three different brands of Kalk now with the same issue (BRS, Mrs. Wages, and a chemical supplier on ebay). It's almost as if I'm dosing sodium hydroxide instead of calcium hydroxide. I can't find anything anywhere online about what might cause this or anyone else having this issue. In addition to Ca Mg also drops insanely fast when dosing Kalk. In theory you're supposed to lose about 5 ppm of Mg for every 100 ppm of Ca but for me it's more like 2:1. I see no significant growth, cloudy water, or limescale buildup that could account for the precipitation (if that's indeed what's causing it). It almost seems like the Ca/Mg are bonding with something other than CO3 and being removed from solution somehow. But that seems impossible. My PH is stable at 8.3 throughout the day. I mix 2 tsp of kalk per gallon of RO water and use a BRS peristaltic pump on 24/7 to dose 1600ml of kalk per day at a rate of 1.1 ml per minute. I do use RO water at 20-25 TDS instead of RO/DI because DI is just too expensive for me to run with a TDS that high (long story for another thread). Please help. I really want to use kalk due to its convenience, the fact that it yields perfectly balanced Ca/Alk, and it doesn't add salinity over time. But due to this issue I have had to abandon it.

TLR: Why does my calcium and magnesium always drop off a cliff while alkalinity remains normal when using kalk?

 

[Chinook]

My calcium always drops alot faster aswell and I'm using randys 2 part. But was the same when using C-balance

 

[Adam Obenauf]

I have a different issue then.

 

[Randy Holmes-Farley]

The effect you are seeing is definitely not from the limewater (kalkwasser).

If anything, it tends to allow calcium to very slowly rise over time when maintaining alkalinity because it exactly matches the amount of calcium tot he amount of carbonate generated, but since magnesium and strontium get into precipitating calcium carbonate in place of some of the calcium, the actual demand is not precisely balanced, and calcium tends to slowly rise. I observed that in my tank over many years, and used a lower calcium mix (normal IO) for that reason.

In this case, it might be testing error, or water changes with a lower calcium mix. If you are actively using organic carbon dosing or growing macroalgae to reduce nitrate levels that are high, that can also raise alk and not calcium.

What salt mix are you using?

 

[Adam Obenauf]

The effect you are seeing is definitely not from the limewater (kalkwasser).

If anything, it tends to allow calcium to very slowly rise over time when maintaining alkalinity because it exactly matches the amount of calcium tot he amount of carbonate generated, but since magnesium and strontium get into precipitating calcium carbonate in place of some of the calcium, the actual demand is not precisely balanced, and calcium tends to slowly rise. I observed that in my tank over many years, and used a lower calcium mix (normal IO) for that reason.

Yeah I figured as much. If this effect wasn't so bizarre and difficult to explain I wouldn't have wasted your time asking.

In this case, it might be testing error, or water changes with a lower calcium mix.

It's not testing error. Three different sets of unexpired test kits give me the same results. And the corals stop growing once the levels start dropping.

If you are actively using organic carbon dosing or growing macroalgae to reduce nitrate levels that are high, that can also raise alk and not calcium.

Please elaborate.

What salt mix are you using?

Reef crystals. I will test it the next time I make a batch. But I ran the numbers and the saltwater would have to have almost no calcium at all in order to drop my levels by 50-80 ppm a week. Plus if that's the case then why didn't I observe this when doing two part dosing? I really doubt that this is the answer.

 

[Randy Holmes-Farley]

Denitrification increases alkalinity, exactly as much as nitrification lowers it. So at steady state there is no effect, but if nitrate is dropping, alk can rise.

 

[Adam Obenauf]

Yes but the effect would only be temporary, no? Since the production of that nitrate via oxidation releases identical amounts of acid. My tank has always read 0 nitrate but I dose vinegar anyways because it reduces my algae growth. I do also run a macro refugium.

 

[mazoli]

Denitrification increases alkalinity, exactly as much as nitrification lowers it. So at steady state there is no effect, but if nitrate is dropping, alk can rise.

Can you please explain this or point to reference where this is explained. This is new for me, and very interested why this happens. Thanks.

 

[Randy Holmes-Farley]

Can you please explain this or point to reference where this is explained. This is new for me, and very interested why this happens. Thanks.

When Do Calcium and Alkalinity Demand Not Exactly Balance? by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2004-12/rhf/index.htm

Alkalinity Decline in the Nitrogen Cycle

One of the best known chemical cycles in aquaria is the nitrogen cycle. In it, ammonia excreted by fish and other organisms is converted into nitrate. This conversion produces acid, H+ (or uses alkalinity depending on how one chooses to look at it), as shown in equation 1:

1. 
   (1) NH3 + 2O2 --> NO3- + H+ + H2O

For each ammonia molecule converted into nitrate, one hydrogen ion (H+) is produced. If nitrate is allowed to accumulate to 50 ppm, the addition of this acid will deplete 0.8 meq/L (2.3 dKH) of alkalinity.

However, the news is not all bad. When this nitrate proceeds further along the nitrogen cycle, depleted alkalinity is returned in exactly the amount lost. For example, if the nitrate is allowed to be converted into N2 in a sand bed, one of the products is bicarbonate, as shown in equation 2 (below) for the breakdown of glucose and nitrate under typical anoxic conditions as might happen in a deep sand bed:

1. 
   (2) 4NO3- + 5/6 C6H12O6 (glucose) + 4H2O --> 2 N2 + 7H2O + 4HCO3- + CO2
   

In equation 2 we see that exactly one bicarbonate ion is produced for each nitrate ion consumed. Consequently, the alkalinity gain is 0.8 meq/L (2.3 dKH) for every 50 ppm of nitrate consumed.

Likewise, equation 3 (below) shows the uptake of nitrate and CO2 into macroalgae to form typical organic molecules:

1. 
   (3) 122 CO2 + 122 H2O + 16 NO3- --> C106H260O106N16 + 138 O2 + 16 HCO3-
   

Again, one bicarbonate ion is produced for each nitrate ion consumed.

It turns out that as long as the nitrate concentration is stable, regardless of its actual value, there is no ongoing net depletion of alkalinity. Of course, alkalinity was depleted to reach that value, but once it stabilizes, there is no continuing alkalinity depletion because the export processes described above are exactly balancing the depletion from nitrification (the conversion of ammonia to nitrate).

There are, however, circumstances where the alkalinity is lost in the conversion of ammonia to nitrate, and is never returned. The most likely scenario to be important in reef aquaria is when nitrate is removed through water changes. In that case, each water change takes out some nitrate, and if the system produces nitrate to get back to some stable level, the alkalinity again becomes depleted.

If, for example, nitrate averages 50 ppm at each water change, then over the course of a year with 10 water changes of 20% each, the alkalinity will be depleted by 1.6 meq/L (4.5 dKH) over the course of that entire time period. This process is one of the primary reasons that fish-only aquaria that often export nitrate in water changes need occasional buffer additions to replace that depleted alkalinity.

While the magnitude of the depletion described in the paragraph above is fairly easy to understand, it also can be converted into units that clarify the imbalance. The impact of alkalinity depletion on the calcium and alkalinity demand balance depends, of course, on the amount of calcium and alkalinity added (and consumed) over the course of that same year.

For a typical reef aquarium (assuming a daily addition of saturated limewater equal to 2% of the tank's volume), the amount of alkalinity added during the course of a year is 297.8 meq/L. Likewise, the amount of calcium added is 5,957 ppm Ca++, given the ratio of 1 meq/L of alkalinity for every 20 ppm of calcium that has been discussed above. If that 1.6 meq/L of alkalinity is added to create a larger demand of 299.4 meq/L over the course of a year, the new ratio for the total demand becomes 19.90 ppm Ca++ per 1 meq/L of alkalinity. Consequently, while this effect of nitrate production on alkalinity is enough to be noticed over the course of a year, it is substantially smaller than the other effects discussed in this article, and is unimportant for aquaria that maintain low nitrate levels.

 

[Adam Obenauf]

Since I consistently have 0 nitrate on my tank year round I can safely rule that out as a source of the imbalance according to that article.

I'll report back here when I get the results after testing my reef crystals saltwater.

 

[Randy Holmes-Farley]

OK, sounds good.

 

[Stigigemla]

When I started reefing again in 2004 with a nano having a very small skimmer I had the same problem. But my pH went higher.
I added about 2 cups each day for 8 gallons. I had one cleaner shrimp and 2 small hermits with some softies.

 

[Adam Obenauf]

Tested my freshly mixed saltwater. Ca/Alk are normal. Calcium/Magnesium continue to drop much faster than they should relative to alkalinity. This makes no sense. The only remaining thing I can think of is if the two part isn't actually balanced. But I did the math and in order for me to be getting the numbers that I am seeing I would have to be dosing no calcium at all which is definitely not the case. I followed the BRS instructions on dosage to the dot when mixing them up so this doesn't seem possible. But I've already ruled out every other possible explanation that you've given me.

The other problem I'm having is I'm dosing over 10x what every site says I should need for a tank this size just to keep alk stable at 7 dKH despite the fact that I see no significant growth in the few small LPS/SPS frags that I have, corraline algae, or any other calcerous organism and no abiotic precipitation on pumps, heaters, or anywhere else. So where is it going? And this has been ongoing for at least 3 years now. My PH does not go above 8.3 ever and I drip the two part continuously at a very slow rate using alternate times with an automated dosing pump. I do see a slow buildup of sand over time in my bare bottom tank (maybe 2 mm per year). But I don't know if that accounts for it or if it's just sand from my fuge slowly migrating to the display tank over time.

For reference I dose 90 ml per day of each solution and according to BRS's site with my 50 gallons of water volume that equates to 17.5 ppm of Calcium per day and 2.5 dKH of alk. I dose 15ml of calcium solution at 12:00 AM, 4:00 AM, 8:00 AM, 12:00 PM, 4:00 PM, and 8:00 PM. So 6 x 15 = 90. I dose 15ml of alk solution at 2:00 AM, 6:00 AM, 10:00 AM, 2:00 PM, 6:00 PM, and 10:00 PM. Again same thing. I've tried many other balanced two part additives though all with the same issues. Including your recipes. And I can't grow coral unless I use this insane amount of solution to keep things from dropping. If I unhook the two part and just use kalk it will drop to 5.6 dKH 350-360 ppm Ca within 1-2 days and the corals will stop growing entirely. It will stabilize there.

 

[Randy Holmes-Farley]

Just to reiterate, there's no sink for substantial amounts of calcium that does not also take out the equivalent amount of alkalinity.

So if calcium is dropping and alk is not, it must be either due to an unexpected source of alkalinity, or water changes.

Bear in mind that even though water changes may have just as much calcium as the tank, some are balanced toward excessive alkalinity. That could make apparent demand for alk seem lower than for calcium. Or if maintaining alk, excessive demand for calcium.

Other sources of hidden alk besides supplements (some of which have it even if they say they do not), include artificial rock, tap water, and reducing nitrate levels (actually declining, regardless of whether they are low or high in absolute terms).

 

[Adam Obenauf]

Just to reiterate, there's no sink for substantial amounts of calcium that does not also take out the equivalent amount of alkalinity.

I know it seems impossible. And yet that is what I am observing.

So if calcium is dropping and alk is not, it must be either due to an unexpected source of alkalinity, or water changes.

Well it's not the water changes. Which I kind of suspected because sometimes I go months at a time without them and still experience the issue. And I don't see any other viable sources of alkalinity.

Bear in mind that even though water changes may have just as much calcium as the tank, some are balanced toward excessive alkalinity. That could make apparent demand for alk seem lower than for calcium. Or if maintaining alk, excessive demand for calcium.

Nope, it's actually unbalanced slightly in the opposite direction. 9.5 dKH 440-450 ppm Ca when I tested freshly mixed saltwater. So actually water changes are slightly excessive in Ca, not deficient.

Other sources of hidden alk besides supplements (some of which have it even if they say they do not), include artificial rock, tap water, and reducing nitrate levels (actually declining, regardless of whether they are low or high in absolute terms).

I have discontinued all other dosing and observed no change. The tank does not use artificial rock and has had no new items (including rock) introduced in over a year. The RO water I use has a tiny amount of alkalinity, but not enough to effect the tank this much (<1 dKH). My tank has always had 0 nitrate so that can't be it either.

I would like to add something else to my what the heck list now. The drop in both Ca and Alk seems to be proporitonal to how much I add. I raised the dKH from 7 to 8 one day by slowly dripping a baking soda solution (1/4 strength) and measured it 15 minutes later to verify. The next day at the same time it was down to 7 dKH. The next day I tried raising it from 7 to 9.5. 24 hours later back down to 7dKH. The next day I tried raising it to 12 dKH. Same thing down to 7 dKH 24 hours later. It's as if any alk or Ca added past a certain point is quickly removed from solution. I checked my Mg and PH and they are both normal. This is insane. I'm now adding 25x what a SPS heavy reef should be using and it's still not staying up.

 

[Randy Holmes-Farley]

I'm not sure what you could mean you are adding 25 x what a reef would use.

Reef tanks use 0.5 - 4 dKH per day.

You are adding 100 dKH of alkalinity per day? No.

The higher you push alk the higher the demand for it. I don't consider a few dKH per day to be crazy.

 

[Adam Obenauf]

I'm going based on what BRS recommends for their two part.
0.1ml/gal/day for softies
0.2ml/gal/day for LPS or mixed reef
0.3ml/gal/day for SPS

For 50 gallons of water this equates to 5, 10, and 15 ml/day. Whereas I need over 300ml per day just to keep it at 7 dKH. Ok not 25x, it's actually 20x. But still that's a lot. In fact BRS recommends no more than 1.5dKH per day to be added but I'm already at 4x that much. If you think this is normal then I likely need to adjust the dosages and just find some way to deal with it. Still I wouldn't expect such high demand when there is no clear sink for it. No buildup on heaters/pumps, no corraline, barely any growth on the few small frags I have.

 

[Randy Holmes-Farley]

I'm going based on what BRS recommends for their two part.
0.1ml/gal/day for softies
0.2ml/gal/day for LPS or mixed reef
0.3ml/gal/day for SPS

For 50 gallons of water this equates to 5, 10, and 15 ml/day. Whereas I need over 300ml per day just to keep it at 7 dKH. Ok not 25x, it's actually 20x. But still that's a lot. In fact BRS recommends no more than 1.5dKH per day to be added but I'm already at 4x that much. If you think this is normal then I likely need to adjust the dosages and just find some way to deal with it. Still I wouldn't expect such high demand when there is no clear sink for it. No buildup on heaters/pumps, no corraline, barely any growth on the few small frags I have.

Those are not the "normal" doses. They are very VERY low starting doses. It might even be a typo. Normal doses would be more like 1-3 ml per gallon per day. They use the two part I invented, so I am very familiar with the dosing. 1 mL/gallon is only 1.4 dKH per day. Even coralline algae alone in a soft coral tank can consume more than that.

 

[Adam Obenauf]

Thanks for the reassurance. This poses another problem though. That's also a lot of sodium chloride being added. At my current rate of 6dKH per day:
~107 ppm CaCO3
~43 ppm calcium
~64 ppm CO3
~49 ppm Na
~70 ppm Cl

So around 120ppm of salinity is added per day or about 0.375% at 32 ppt salinity. That's around a 2.63% gain in salinity a week! A 5-10% WC every week with low salinity water wouldn't be anywhere close to enough to offset that. You would have to remove saltwater either manually or by skimming and replace it with freshwater at a pretty high rate. And since that dilution reduces levels for all ions wouldn't trace elements go down over time until your salinity was almost all NaCl? No wonder you guys do so many water changes. I guess that's an advantage then for a calcium reactor since it doesn't dump huge amounts of NaCl into the tank.

 

[Randy Holmes-Farley]

Using a two part does boost salinity. It is often offset by skimming (depending on how wet you skim), or occasionally removing some salt water and replacing with fresh. Water changes with lower salinity water will also often do the trick. If you changed 10% weekly with water that was 10% low in salinity (say, sg = 1.0234 instead of 1.026) that will reduce salinity by 1% weekly. I show below that that amount will more than offset what the two part is adding at the dose in the example.

I discuss it here, where I gives the recipe for a two part:

An Improved Do-it-Yourself Two-Part Calcium and Alkalinity Supplement System by Randy Holmes-Farley - Reefkeeping.com
http://reefkeeping.com/issues/2006-02/rhf/index.php

from it;

"After one year of adding 8 ppm of calcium and the accompanying 0.4 meq/L (1.1 dKH) of alkalinity per day (41 mL of both parts per day or 4 gallons of both parts per year in a 50-gallon aquarium, including the effect of the magnesium part #3A, 2440 mL/year), the following residue (Table 2) would remain after calcification and adjustment for salinity (there is roughly a 32% rise in salinity over a year using this addition rate without water changes)."