Calcium & Alkalinity supplementing methods

How do you maintain calcium and alkalinity?

  • Water changes

    Votes: 3 13.6%
  • Kalkwasser

    Votes: 5 22.7%
  • "2"-part (including Triton)

    Votes: 8 36.4%
  • Calcium reactor

    Votes: 3 13.6%
  • Mixture of above (please specify with reply)

    Votes: 2 9.1%
  • Other (did I miss one? please specify with reply)

    Votes: 1 4.5%

  • Total voters
So I've been thinking about various ways to supplement calcium and alkalinity (and magnesium) into my upcoming project tank which will be full on stony corals, softies go in the separate anemone tank. Mike's (Coral Reefer) tank thread comments just made me think of some of the thoughts I've been having and just wanted to express some of them.

Not going to speak about specific equipment other than refer to size/demand scale of things as equipment can vary quite a bit.

Ultimately there are four methods of maintaining your tank for calcium and alkalinity,water changes, "2" -part dosing, kalkwasser & calcium reactors, there are pros and cons to all, but almost all could be used to accomplish the same thing, there also is the option of using multiple sources. What's good for one person for their tank setup, lifestyle, desire for work may differ from others, that said I would love to hear various opinions/methodology you live by.

It goes without saying that none of these methods are truly "set it and forget it" in the sense you can find your amount and not have to worry about it, each one should be accompanied with regular water testing in some fashion. While you might get to a nice area where you're fragging as much as is growing you never want to just walk away and ignore.

Water changes

Pros: No specialized equipment necessary, helps add in additional elements, "cleans" the tank.
Cons: Salt mix must have elevated levels, most of those "additional elements" are largely unknown by the end user, not as feasible for large demand systems.

Not a fan of water changes to maintain anything in our tanks other than elements that are "undetectable" (although things like Triton is making it more detectable). As higher demands require more water to be changed it gets pricey quick in a hurry. Plus you need to picky about your salt mix because it needs levels above what you want to keep in your tank, it's simply a math problem, if you have a density of X of something in your tank, and you replace out with a density of Y of new salt water, the mixture of the two is going to be higher than X yes, but less than Y. So if your salt mix has the perfect calcium & alkalinity levels when you mix it fresh, your tank water will never have those perfect levels unless you do a 100% water change all at once (not advisable).

Pros: Relatively inexpensive, equipment cost moderately small, ease of use, raises pH, assists with evaporation replenishment
Cons: Limit on how much you can add, caustic chemicals handle with care, if using a pump based "reactor" maintenance/replacement tends to be quicker, only adds calcium and alkalinity

I gotta say, I love Kalkwasser, the simplicity of how it works is just great. Add your powder to water, and drip in, done. pH raising is a mixed blessing as you can use it to counter act low pH moments, night time, too many fricking people breathing around your tank, or using a calcium reactor, that said the other side of that coin is that raises pH if whatever mechanism you use fails and it auto floods you're in for a world of hurt, and then the other side is there is a maximum limit to how much you can add to your tank, it's not like upsizing a reactor will help either if your demand is higher than the amount of kalkwasser you can safely add to keep your pH under a certain amount you are limited by how effective this is and this is a real limitation too. That said it is great early on when you don't have much of a demand, the increased pH will also increase the calcium and alkalinity uptake and allow your little frags to grow into slightly larger frags much faster. Of course this only adds calcium and alkalinity, so any magnesium needs (and corals do need it) will need to be done separately, ditto for any "trace elements". That said this is a really good thing to use in conjunction with other methods, and as such other than in a "low demand" tank I wouldn't use it as a stand alone product.

Also note, I mention assisting with evaporation as a pro, you need to make sure you don't use this as your ATO. You need to do whatever dosing you're going to do to keep the levels you want and THEN fill deal with evaporation. The chances of your evaporation level ATO needs matching the exact amount of kalkwasser that you need to add to maintain calcium and alkalinity levels is slim to none, even if you manage to do the chemistry math your tank probably will evaporate different amounts based on various condition (temp, humidity, turbulance, etc).

Pros: Simple as can be, many choices, relatively low equipment need, accidental overdose protection
Cons: Need to add other "parts", relatively short duration between replenishment, possible precipitation issues, possibility of getting "out of balance"

Whether you follow Randy's recipe with BRS supplies or Costco & pool supplies (guilty), use pre-bottled solutions (you're paying mostly for water!) or you jump on board new methods like "Triton" they're all more or less the same. You have separate containers of calcium and alkalinity (and magnesium in the case of Triton) and you drip in what you need. The only real equipment you need is a dosing pump and you can go cheap with a Jebao unit, or higher end with GHL/DoS or other similar units all will perform more or less the same except for maintainance/failure issues. That said I have had a malfunction in the past and overdosed 2- 5 gallon bucket (probably half full) into my tank over night (Neptune's power bar fault... and maybe some corrosion that's kinda my fault.. kinda in that they didn't make IP65, the power was no where near water this was humidity corrosion), and I woke up to a snowy white winter wonderland of a tank which looked cool except for the fact I freaked out by seeing my tank white! Tank did not crash, corals were fine, only casualty was a solon wrasse who was still in his mucus cocoon. Reason? After a set level precipitation occurs and nothing else is added, plus the stuff is "pH" neutral.

So the cons are that you need to turn your 2 part into a 3 part, however I have heard the 3rd part (magnesium) can just be dumped in when you replace your 2 part solutions as opposed to needing more equipment. Depending upon your tank need you might find yourself mixing 2 part more often than you like, on my 180g tank I just used a couple of empty salt buckets and I was good for a few weeks, that said I did notice "crud" on the bottom and not sure if that was undissolved stuff or if it "fell out" while sitting too long and requires constant mixing. Other problems is that if one of your dosers gets clogged or spins at a slightly different rate, the balance between calcium and alkalinity can drift. Also a problem I used to have is that when following Randy's recipe, I'd notice a white cloud when the stuff hit the water (precipitation) and all that cloud is stuff that no longer is going into my tank, not sure if it was specific to my tank (pH was too low?) or what, but a quick solution is I just made half strength batches and all was good, luckily my evaporation levels were far greater than the amount of 2 part I put in. I'm not sure if it is possible to have too much demand though that the 2 part need is larger than ATO needs.

Calcium Reactor
Pros: Adds everything, very long lasting before refills needed
Cons: Expensive equipment, lowers pH, possible "end of life" issues, sized for a specific tank size(?), you turn your corals into cannibals!!!

Calcium reactor is simple in it's design, you have old coral skeletons (except with the DaStaCo $etup$), you add CO2 to lower pH so they dissolve, and everything your corals need? Well you just dissolved it from dead corals so you're good to go! All calcium reactors work on the same basic principles too, there's at least one chamber for media, CO2 canister with a regulator of some sort, a pump to move water through your reactor, and another pump to put said reactor liquid into your tank, different models will have varying costs based off quality, name brand and certain other "quality of life" (aka bells and whistles) additions. Most difficult part is to find a happy balance of CO2 addition that keeps the pH at a level you're happy with, too low pH you go through media too quickly and turn to mush, too high pH and you're not dissolving media, once done it's similar to other methods you simply need to know how much demand your tank has and drip that amount into your tank. Often clammored as the best method for very heavy demand tanks, and by best I think people mean you can leave the reactor by itself for much longer periods without needing to replenish your media compared to kalkwasser and 2 part.

Cons are up there though, if you go cheap with a calcium reactor you're still putting in a pretty hefty investment, the equipment compared to other methods is by far much more expensive even if you compare the cheapest calcium reactor setup (new stuff, no fair finding great deals off used equipment! :D) with the highest end dosing pumps (that you'd realistically use for 2/3-part... no masterflex nonsense!) your CaRx setup is probably still more expensive. I have yet to see a detailed analysis of media costs over time, it may well end up being cheaper than 2-part or kalkwasser but of course it depends upon what you source (BRS supplies are going to be much cheaper than pre-bottled solution). pH is another issue to worry about, because lowering your pH is almost never good on a reef tank, with small enough dosing and enough aeration on the tank it's not an issue but dose too much and it can be problematic, also as a CO2 canister gets low I have heard of issues with it "burping" and dumping a bunch of CO2 into your CaRx which makes the pH lower which is what you're dripping into your tank, however with properly calibrated probes it can be mitigate, not sure if this is only a problem with certain regulators but either way I'd guess more pricey for more protection. pH probes in the tank is probably good backup plan too, connected to a valve (or valves) having the ability to absolutely shut off the adding into your tank if the pH drops too low is probably a good thing.

Ending thoughts
So those are my thoughts, if it seems the writing style changed it's because there was 5-6 hour break from when I started due to parental responsibilities so all of my thoughts I originally had may be a bit muddled. With my 200 gallon tank I'm definitely doing kalkwasser to start with, and probably going to stick with 2 part just for the simplicity aspect of it, and I already have all the equipment needed, although I'll definitely leave space for a calcium reactor "just in case". Those Vertex ones are go on sale everytime BRS has one, although MACNA is just around the corner and I love to see what's out there instead of just what a particular online store has for sale (see the LFS size problem exists within the online realm as well, just on a larger scale).

Any other thoughts? Comments?


Supporting Member
For 2 part, look at the Triton Core 7. You will need 4 dosers but it takes care of trace as well.

2 stage regulators aliviate the end of tank dump.

The best way, imo, to run a CaRx is NOT to use a pH probe to control CO2 dosing. Instead, use a good reliable pump and regulator. But most importantly is a very fine metering valve on the regulator.

The idea is to use the regulator and metering valve in conjunction with the steady dosing pump to fine tune the effluent. The solenoid will be always open if tuned correctly. This way, you are not at the mercy of a potentialy faulty or poorly calibrated probe. You also do not use a needle valve on the effluent line, you use the dosing pump to control the amount of effluent flow and eliminate the clogging issues with the needle valve.

You still use a pH but as a last stop safety.

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Combination. Complex to set up, but very simple to maintain.

Automatic water changes:
DIY auto-water exchange system. Not a huge percentage, but decent.
A very simple way to keep all minor and trace elements in check.
Basically, this deals with everything except Alk+Ca.
Also reduces pollutants a bit, and generally keeps everything stable.

Kalk reactor:
This is run off a doser, constant interval, not top-off.
This is set to about 1/2 of normal evaporation rate, and never adjusted.
Really helps push PH up, reduces phosphates a bit, and a cheap way to dose.

DIY 2 part: Alk + Ca only
Runs off dosers.
This is for tweaking Alk/Ca as needed, as corals come and go.
Since it is a small part of the system, lower volume, and much lower effort and risk.


Water changes
Cons: Salt mix must have elevated levels, most of those "additional elements" are largely unknown by the end user, not as feasible for large demand systems.

Most salt mixes are relatively close to normal sea water except for elevated Alk + Ca + Mg.
In our reef tanks, Alk + Ca are really dominated by your corals use / additional dosing.
Mg level is largely irrelevant unless you are pushing Alk/Ca/PH extremes.
So basically - it does not really matter.

Usually "premium" mixes have elevated levels. And as a bonus, they add organics. (AKA pollutants)
Consider a cheaper brand.

You can pretty easily mix up a batch of salt mix and have it ICP tested if you really care.
Well I don't know about most salt mixes, and I literally don't know about most. But it is something you need to be aware of, if you use Instant Ocean for instance it most definitely doesn't have elevated levels, if you use something like Fritz then you better use it quickly or else your alk might take a nose dive, other salt mixes are probably good (I used to use Salinity) but I don't know if they all tell you what they are supposed to mix to. plus if you're getting "premium" mixes it really starts to make water changes as a very poor (expensive) way to maintain the big 2 elements.

ICP test on my salt mix? I'm not going to pay $30-40 just to find out what the manufacturer should tell me :D Speaking of which, when is the Apex going to get an ICP module? :D


Standard IO has elevated Alk.
They all vary.

Considering what I spend on my aquarium, and how rarely I change salt brands, $25 to know seems cheap.
But yes ... it is seriously annoying that the manufacturer does not post that.
Well if you really care a simple Ca and Alk test you can do at home should be more than sufficient, the big question mark (at least for people like me) is when you store a large amount how do the numbers change. One reason I won't use Fritz salt even though they seem to be a major sponsor at many reef events over the past couple years.
Sfsuphysics.. I would consider any transition point as a chance for issues. (Kalk->2 part->carxr)
CalReactor after kalk dosing, sort of like rygh describes, would get my vote. And an electric co2 regulator, if in budget, is a must.


2 DOS pumps (4 heads):

1. Aquaforest 1+
2. Aquaforest 2+ dissolved with Aquaforest Reef Minerals
3. NoPox
4. AcroPower (aminos)

My Mg is super high from the Aquaforest Reef Salt, and nothing ever uses it it seems, so I don't dose Mg, but everything else in Aquaforest 3+ is in "reef minerals," so I just dissolve that into 2+.

NoPox is to keep dinos away (long story, but it works great)

AcroPower might be snake oil, but I'm using it without any issues. New SPS nubs look good.

Aquaforest 1+, 2+ also has trace elements and all sorts of stuff. I think dosing 1+, 2+, 3+ is equivalent to a lot of those AIO dosing solutions.
Sfsuphysics.. I would consider any transition point as a chance for issues. (Kalk->2 part->carxr)
CalReactor after kalk dosing, sort of like rygh describes, would get my vote. And an electric co2 regulator, if in budget, is a must.
Well changing methods is absolutely going to be something that has a potential for introducing "problems" simply due to the different mechanisms involved, but you could say the same about changing salt mixes, changing nutrient export methods, or even changing lighting. So in that sense starting out with the "final product" is something to consider, however given the expense of the entire CaRx setup it might put people off and to be honest unless you absolutely load your tank with frags on day one (which does happen) then a CaRx may be WAY overkill for your tank.

That said I think if I did feel I had the demand for need of a CaRx I would absolutely run it in conjunction with kalkwasser just to try and offset the pH lowering, plus having pH a little on the higher side has been shown to accelerate coral growth.

And those electronic CO2 regulators unfortunately I think there's only one on the market "Carbon Doser" fortunately it is a simple design that you could make yourself, or if you don't want to there's a guy who used to make them (has a webpage, and has gotten Cease and Desist letters :D) and he sells the whole setup for significantly cheaper


Art look like you're going all in with Aquaforest on your tank :D
They got me with a huge sale on BRS last year. Nothing terrible and I like how the salt mixes (other than high mg). But yeah, sticking to one brand seems like a nice way to dose everything needed.


Hey if it works, and you're tank isn't having problems no argument from me whether you stick with Aquaforest, Jebao, or Fischer-Price :D
So far so good! Hoping it will stay that way =)

Also, doing this type of dosing etc. is pretty sustainable for a small tank like mine. Going bigger would get much more expensive if I dosed this stuff all the time.


Staff member
So far so good! Hoping it will stay that way =)

Also, doing this type of dosing etc. is pretty sustainable for a small tank like mine. Going bigger would get much more expensive if I dosed this stuff all the time.
i was dosing 123 but had to stop since it was not ideal for my larger system.


Cynical opinion:

Aquaforest 1+ says it contains: Ca, Sr, Ba, Co, Mn, Cu, Fe, Zn, Ni, Cr.
If you do not do many water changes, those other elements would accumulate eventually.
Notice the Cu (copper) for instance.
So it would be scary to use if the trace element levels were high.
But if levels are low enough not to cause problems ... then they are probably low enough not to matter either.
Which means .... it is just marketing.