Randy Holmes-Farley
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Pros and Cons of Alkalinity and Calcium Dosing Methods
How to decide which is best for you and your aquarium.
How to decide which is best for you and your aquarium.
By Randy Holmes-Farley
Supplementing calcium and alkalinity is one of the most important chemistry requirements for most reef aquariums. Deciding which of the many different methods are most suited to your situation involves many different considerations, and the relative importance of each of these varies by aquarist and the aquarium involved. In this article, I will lay out these considerations as I see them, and so thereby hope to assist you in selecting the method you want to use on a new tank, or switch to on an existing tank. Note too that there’s no reason you need to use only one method, and folks often use two, with each helping offset limitations of the other.
In general, I recommend only balanced alkalinity and calcium addition methods, rather than using entirely unrelated additions of each. It is rare to be truly significantly unbalanced unless the demand is very low to begin with. There are a few reasons demand may be somewhat unbalanced, especially due to water changes and impacts from the nitrogen cycle, and methods that allow slight adjustment (say, a two part) will inherently allow making minor modifications while a fixed additive (kalkwasser, AFR, etc.) may require occasional corrections some other way.
This article is a summary for folks wanting an overview of the pros and cons of different methods. I have much more detailed discussions of the details in other articles, such as these:
https://www.reefedition.com/the-many-methods-for-supplementing-calcium-and-alkalinity/
https://www.reef2reef.com/ams/how-a...-calcium-system-works-and-why-it-matters.958/
These are the aspects of the methods that I will be addressing:
- Cost for the materials
- Cost of equipment
- Safety of the materials to the aquarist
- Ease of attaining the materials
- Storage issues
- Time needed by aquarist to set up and adjust
- Complexity (hard to understand effects and dose tuning)
- Anything else added, such as magnesium or trace elements
- Effect on pH
- Limitation on amounts dosed
- Problem scenarios (e.g., overdose)
- Any measurement complexities
- Any other effects (e.g., organic carbon dosing effects; salinity changes)
These are the methods I will assess:
- Limewater/kalkwasser/calcium hydroxide
- One-part additives using organics (e.g., All for Reef; Carbocalcium; formate; acetate)
- Two Part methods (there are many good brands to pick from, such as ESV B-ionic)
- Three Part Methods (there are many good brands to pick from, such as Tropic Marin Balling, DIY, and hybrids)
- CaCO3/CO2 reactors
https://www.reefedition.com/the-many-methods-for-supplementing-calcium-and-alkalinity/
Summary Table
This color-coded table is just my opinion and there are cases where a particular use may be different than I indicate. The table may be all you need to help guide your decisions as the remainder of the article just discusses the details of all of these entries.
Colors from best to worst are:
Purple means it is too variable to rate as a single color
Summary Table Comments:
Safety: a two/three part using hydroxide is red, carbonate is yellow, bicarbonate is green.
pH: green is pH raising, yellow is slight lowering to neutral, orange is pH lowering
Side effects: AFR/carbo calcium: possible carbon dosing effect and O2 lowering; 2/3 parts: salinity rises
Cost of Materials
For costs, I thought a single table might be the best way to show it. However, cost is a very complicated topic since it depends on where one buys them, what quantity is purchased, if shipping is extra or not, and how much one actually uses. For that reason, I think qualitative values will be most generally useful for this purpose. I have included some actual costs from one supplier (BRS) that sells many of these to see what I mean by relative costs. For a multipart product, it means for all parts. In this case, it is the cost to boost 100 gallons by 2 dKH one time.
Folks considering just one or two methods can then double check costs from their preferred source for the amounts needed.
Cost calculation info:
Kalkwasser; 10 grams calcium hydroxide
AFR: 126 mL
Carbocalcium: 17.6 g
TM Balling 272 mL of Parts A and B and C. A uses 20.7 g ($0.32); B uses 20.6 g ($0.26); C uses 6.5 g ($0.12)
DIY three part food grade baking soda ($17/15 pounds; 22.7 grams, costs $0.06) calcium chloride (food grade) $71 for 50 pounds; 19 g for $0.06 ) Balling Part C (from above, C uses 6.5 g ($0.12)
DIY three part industrial baking soda calcium chloride Mag Flake, Epsom salt
B-ionic 96.6 mL
CaCO3/CO2 media 13.5 g
Equipment Cost
Necessary equipment is an additional cost for these methods. One can do some of them manually once a day, and thus there is no required equipment cost aside from testing equipment to know how much to dose.
Kalkwasser requires some sort of pump, a reservoir, and a reactor (if used). I put kalkwasser in my ATO. You may also need a mixing pump to dissolve it, such as a cheap powerhead.
A two or three part can be manual once a day, or automated with dosing pumps, one for each part. These cost $50-$250 each. They can often be dispensed from the container they come in.
A one part such as All for Reef or Carbocalcium can be manual once a day, or automated with a dosing pump for $50-$250. It can be dispensed from the container it comes in, unless you make it from powder. You may want a magnetic stirrer to help initially dissolve it if you do the powder route. The magnetic stirrers can be fairly inexpensive.
A CaCO3/CO2 reactor requires a lot of equipment: a CO2 cylinder, a reactor, a gas cylinder regulator, a reactor water feed pump, and some sort of control, either by pH or bubble count. A reactor is $200-$500, a regulator and controller can be $400, a feed pump might be $100-200, and an additional secondary chamber is $50-100. These costs greatly offset the very low media costs for the system, but still may be the least expensive option over time in a large aquarium. Before embarking on getting such a reactor, read up on exactly what you need and want to get so you can price it out to suit your system needs.
Figure 1. A Deltec calcium reactor used by Reef2Reef member Jaculus.
Materials Safety
There are two main issues with material safety. One is children that might get into them, and the second is for reasonable adults. Of course, safety issues for adults apply even more so for kids.
With small kids around, all chemicals should be protected from their reach. A lock on the storage is not unreasonable.
The worst chemicals used in alk and calcium methods with respect to normal adult usage are likely to be:
1. Sodium hydroxide. By itself or in a two part. Very high pH and damaging to tissue, especially eyes. Add slowly to cool water as it generates heat when dissolving.
2. Calcium hydroxide (limewater/kalkwasser), similar to sodium hydroxide, but less so due to the limited solubility. More dusty, however, and dust inhalation should be avoided.
3. Sodium carbonate. By itself or in a two part. Reasonably high pH and corrosive. Not as bad as 1 or 2, but still a concern.
4. CO2 cylinders used with CaCO3/CO2 reactors. The cylinders carry some risk, and should not be too old.
Figure 2. A calcium carbonate/carbon dioxide reactor used by Reef2Reef member jblsi.
Ease of Obtaining Materials
Obtaining chemicals is mostly only an issue when making DIY additives, and the hardest to find at very low cost/suitable purity is likely to be magnesium chloride. It is readily available at higher cost (such as at BRS).
Storage
Aside from issues relating to safety of storage (e.g., keeping all of them away from children), one other storage issue is that some alkalinity additives are near their solubility limit, and if they get cold, such as in a garage, they may precipitate significant solids that will require warming to redissolve.
Additionally, storage of kalkwasser is complicated by its necessarily low potency. One can either make it in situ in a reactor (thought that can haves issues of potency control and increases costs), refill a small reservoir frequently, or use very large reservoirs. I chose the latter, using 3 x 44 gallon brute cans plumbed together to give enough for a month or two. That takes a lot of space, such as in a basement or garage.
Storage of CaCO3/CO2 systems is complicated by the need for the cylinder, the reactor, the controls, and feed pump.
Figure 3. All for Reef being dissolved for mixing by Reef2Reef member Glenner’sreef.
Aquarist Setup Time
- Kalkwasser takes some time to make a reservoir of material, or maintain a reactor with appropriate levels of undissolved calcium hydroxide. In my large reservoir, it took a total of about 15-30 minutes once a month or two, to make a new batch, so not a big deal.
- Liquid additives (two parts, AFR, etc.) are generally ready to go or need some minimal dilution effort. Some methods require a bit more mixing time (carbocalcium powder, AFR powder, etc.).
- A CaCO3/CO2 reactor requires a substantial amount of time to set up, and also to tune to the needs of the tank, compared to all of the other methods described here.
Complexity
This section is a bit of a catch all for how much an aquarist needs to know to use the method. A one-part additive such as All for reef or Carbocalcium is easiest. A DIY requires more understanding than a complete commercial product, and a three part may require more understanding of what to dose when than a one or two-part system.
- Kalkwasser requires some knowledge about doses and how they relate to pH and alkalinity.
- A CaCO3/CO2 reactor is the most complex of these and requires more understanding of how it works, how to tune it, when to replace media, etc. Once it is set up and running, however, the effort required can be minimal for an extended period.
Figure 4. A typical two part dosing setup using ESV B-ionic. This system was set up by Reef2Reef member Reefiniteasy.
Anything Else Added
What else besides calcium and alkalinity is added is a topic that very often confuses users, and they can come away with a misunderstanding.
Limewater/kalkwasser adds essentially nothing besides calcium and alkalinity. Products touting magnesium in it are not giving a true story since they can actually contain less magnesium than “pure” calcium hydroxide products, and in any case, magnesium will not dissolve into kalkwasser since magnesium has very low solubility at the high pH of limewater/kalkwasser.
All for reef and some two-part, systems add various elements designed to help offset demand in the aquarium. These include a number of trace elements. A reef tank may or may not need any other trace elements.
Tropic Marine Balling, DIY 2/3 part systems, and ESV B-ionic may incorporate other elements (notably in Balling Part C, Aquaforest Mineral Reef Salt, or both parts of ESV B-ionic), but these are not designed to offset consumption. They merely deal with the salinity rise and corrections effects. A tank using these may well need additional trace elements. That topic is explained extensively here:
https://www.reef2reef.com/ams/how-a...-calcium-system-works-and-why-it-matters.958/
CaCO3/CO2 reactors also add some additional elements, but remember these are ONLY those elements that get into the coral skeletons or other calcium carbonate media used. It is not replacing trace elements that are incorporated into tissues or soft corals, macroalgae, etc. A reef tank may or may not need any other trace elements.
Figure 5. Overdosing kalkwasser can lead to cloudy water due to precipitation of calcium carbonate.
pH effects
A useful side benefit of some ways of dosing alkalinity is the effect on pH, which can range from pH lowering to significant pH raising.
- A CaCO3/CO2 reactor adds a lot of CO2 and that CO2 tends to lower pH.
- Hydroxide gives a big pH boost per unit of alk added. It is present in kalkwasser, DIY2/3 parts, and a few commercial 2/3 part systems.
- Because of these last two points, many aquarists combine kalkwasser (for the pH boost) and CaCO3/CO2 reactors (for a big amount of alk and calcium) in high demand systems.
- Carbonate gives half the pH boost of hydroxide, and is present in many commercial and DIY 2/3 part systems.
- Bicarbonate gives a slight pH drop when added to seawater. It is present in some commercial and DIY 2/3 part systems, such as Tropic Marin Balling.
- Organic forms of alkalinity (such as formate in All For Reef and Carbocalcium) give a pH lowering effect. Formate is identical to use bicarbonate in this pH lowering regard. Acetate gives a larger pH lowering. The polygluconate, which Seachem doesn’t mention the alk effect of in Reef Calcium will cause a pH lowering if and when it is metabolized.
Figure 6. A typical dosing setup for a three-part system.
Limitations on Amount Dosed
Aside from being able to afford the materials and equipment, the only dose limitations are:
1. The low potency of kalkwasser causes it to be limited by the evaporation rate. If 1% of the tank volume is evaporated each day, one can add about 1.1 dKh of alk and 8 ppm of calcium each day. Some folks try to dose slurries or dry powder, but that is hard to control and use. Another method is to dose more than evaporation and then do water changes with hypersaline (extra salty) water to maintain salinity. That method increases complexity. At the same time, I do not recommend dosing kalkwasser based on pH alone without monitoring alk since alk may get too high in many systems before the pH target is attained.
2. Organic forms of alk can consume O2 as they are metabolized. Tropic Marin says that is how they arrived at the max daily dose of AFR, but they have reportedly not seen problems at higher doses last I heard. If a reef tank has high aeration and dosing is spread out, it may not be a real limitation.
3. A very high pH alk additive (say, a hydroxide based two part) could possibly drive pH too high if the demand is high and aeration is not sufficient. More aeration will reduce that problem. Like with kalkwasser, I do not recommend dosing based on pH alone without monitoring alk since alk may get too high in many systems before the pH target is attained.
Overdose Concerns
Overdose concerns are highest with very high pH alk additives, such as kalkwasser, or carbonate or hydroxide based two parts. Hydroxide based two parts may be the highest risk since the overdose could be much more severe due to the potency and very high pH effect. Have confidence in your dosing methods before using these. When I used kalkwasser, my pump was sized and set mechanically so that it could not dose more than about twice what I routinely dosed, even if it was stuck on 24/7.
Sucking in calcium hydroxide powder mud from the bottom of a kalkwasser reservoir is another overdose scenario, and I had it happen a few times. Nothing died in my case, but it was stressful to me and the creatures. Keep the intake off the bottom.
An overdose of the organic alk additives (e.g., AFR) can drop O2 and will boost alk over the next day or so. If it happens, maximize aeration.
Figure 7. Baking soda is a mainstay of DIY two part systems. It starts as sodium bicarbonate, which can be used directly, or baked in a home oven to product sodium carbonate, which gives a higher pH boost.
Measurement Complexity
There are two main measurement complexities:
1. The organic alk additives (AFR, carbocalcium, acetate) do not immediately show alk when testing the water. It requires time for bacteria to metabolize the organic into bicarbonate to reliably detect (and for corals to use) the alkalinity. That delay may also complicate automated measurement and dosing systems, so be wary that such a device may overcorrect if measurements are made too soon after dosing.
2. The other measurement complexity relates more to setting up the dosing systems, but often one needs to know the potency of the dosing solution, and that can be complicated to control in the case of kalkwasser. One needs appropriate tools (best is a conductivity meter than can read 5-11 mS/cm) if one wants to know the potency, especially when using a reactor.
Side Effects
There are two main side effects to note, in addition to pH effects noted above.
1. All two/three part systems will raise salinity since the main components are calcium chloride and sodium bicarbonate/carbonate/hydroxide. The exact rise will depend on the formulation, but is around 29% over a year when dosing 1.1 dKH per day and doing no water changes. That equates to 35 ppt rising to 45 ppt or specific gravity = 1.026 to 1.034. Obviously, that’s a large increase and folks should monitor and replace tank water with RO/DI to offset it if skimmers and water changes do not keep salinity in check.
2. Organic additives (AFR, carbocalcium, acetate) have an O2 lowering effect, which is larger the larger the dose. Proper aeration will mitigate this effect.
Conclusion
There are many suitable ways to maintain alkalinity and calcium in reef aquaria. Which methods are best will depend on your husbandry time available, your budget, and your system (including both what is in it and its size). I hope this summary may be able help guide some decision making on what is best for you personally.
Happy Reefing!
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