Unbalance Na/Cl-based products question

[arking_mark]

@Randy Holmes-Farley

When does unbalanced Na/Cl-based dosing impact a reef tank?

I've always tried to practice balance dosing to keep my parameters in line with natural or at least within acceptable ranges.

To me balanced dosing = keeping the ionic concentrations.

For instance, typical 2-part dosing = Calcium Chloride + Sodium Carbonate/Bicarbonate.

Since sodium and chloride aren't really depleted in a real tank, dosing 2-part replaces depleted Calcium and Alk...but increases Na and Cl concentration. (3-part strives to fix this by proportionally adding the other missing components. Some even try to account for known depleted trace ions.)

Many other products we dose are Na/Cl based.

As we keep these tanks for many many years, at what point does this type of unbalanced dosing have an impact? Is there a level of increased Na or Cl that would negatively impact the tank?

I know with Kalk dosing (considered balanced dosing), every 6 months or so, I typically need to reduce my Ca as each tank consumes Ca slightly differently based on inhabitants and maturity of the tank as other components can be incorporated into calcification.

 

[Randy Holmes-Farley]

This is an interesting and complicated question with a variety of different sorts of answers.

As you can see from your posted chart, seawater contains nearly the same number of chloride and sodium ions, with a slight predominance of chloride ions.

Comment 1.

If you use sodium (bicarbonate/carbonate/hydroxide) to boost alk and calcium chloride to boost calcium, and if all of the alk and calcium is going into calcium carbonate, then there is nearly a 1:1 balance between the sodium and chloride accumulating. If it were making pure calcium carbonate, then it would be 1:1. In reality it uses slightly less calcium due to magnesium and strontium replacement in the calcium chloride, so you are adding a little bit less chloride. Thus, over time, there is a small imbalance in that you are adding relatively more sodium than chloride than the ratio present in natural seawater.

However, that strontium and magnesium has to come from somewhere, and if it is replaced with chloride salts, that aspect of the imbalance is reduced to none, but overall, there is still a higher ratio of sodium to chloride added than is present in seawater.

Comment 2.

While one can adjust the relative mix of cations (positive charges such as sodium, potassium, and magnesium) and the relative mix of anions (such as chloride, sulfate, bromide), one MUST always have the same number of total positive and total negative charges in a seawater sample to maintain charge neutrality.

Thus it is not possible to have sodium accumulating and/or chloride declining without something else happening. Assuming you maintain a fixed salinity by removing some salt water and replace with fresh, sodium will rise in relative terms to chloride and in absolute concentration, chloride will decline in relative terms to sodium, but will rise in absolute terms, and EVERYTHIGN else will fall in relative and absolute terms.

To put some numbers on this, I ran some calculations when designing my DIY two part. A number of assumptions went into this and the calculations should not be viewed as perfect, but dosing 1.1 dKH per day and maintaining salinity, sodium rises from 10,760 ppm to 11,010 ppm (2.3% rise), chloride declined from 19,350 ppm to 19,030 ppm (1.7% drop), and here's the kicker: sulfate dropped from 2710 to 2100 ppm, a drop of 22.5%, and that same ratio applies to all other ions not added or consumed by calcification (e.g., potassium).

Comment 3.

The most significant aspect of comment 2 is the fall of everything else, not the small changes in sodium relative to chloride. Thus important ions such as potassium, magnesium, sulfate, etc. all decline. The drop can be very substantial.

There are several ways to deal with this issue.

A. Adding all of these other ions into the alk and calcium parts. Then one will not have these other ions drop. ESV B-ionic takes this approach. Do they make an adjsutment to how these ions are supplied to also correct the small chloride to sodium imbalance, or maybe make it worse? I do not know, they have never said as far as I know, and maybe have not ever considered it. I think the latter is most likely.

B. One can make a salt mix leaving out all sodium chloride. It will still have sodium and chloride from parts of the needed ingredients (such as potassium chloride to add potassium). Adding this mix in an appropriate dose will eliminate the drop of all these other ions. Tropic Marin takes this approach with Balling Part C, and is why I recommend it to use with a DIY two part. Does it also correct for the small sodium and chloride imbalance? Like ESV B-ionic, it could, but I do not know the nitty gritty details of how it is formulated. For example, some could add potassium as potassium chloride, or as potassium sulfate or something else. My guess is that the mix is just ordinary salt mix with no sodium chloride, which solves the ion depression issue, but it is not trivial for me to determine what impact that has on the sodium to chloride ratio in Balling Part C.

C. Final way to correct this issue is to do regular water changes. Aside from 100% changes, this method is not perfect, but it does go a long way to helping both issues (and, of course) can also be applied even with A or B are already used. Craig Bingman modeled these effects many years ago here:

Simulating the Effect of Calcium Chloride and Sodium Bicarbonate Additions on Reef Systems

Aquarium Frontiers On-Line: Biochemistry of Aquaria

Additional Simulations: The Combined Effect Of Calcium Chloride
/Sodium Bicarbonate Additions And Water Exchanges

Aquarium Frontiers Biochemistry of Aquaria

"If you stop doing partial water exchanges on a system managed even in part with pure calcium chloride and sodium bicarbonate, the composition of the water in the tank will continue to increasingly deviate from natural seawater."