Kalkwasser VS Sodium Hydroxide

[DarthChaos]

So, I've been using Kalkwasser for about a year half...and feel like I have a pretty good grip.

My issue is - my Calcium consumption.

I usually top up my kalk stirrer once a week, as I see the pH and Alkalinity start to drop, signifying the kalk is being used up. Issue is, my Calcium consumption has decreased a lot (due to coral lose) and adding more kalk, increases my Calcium level too - which, I don't want.

Someone mentioned to me - about Sodium Hydroxide. PH & Alk boost - without the Calcium. PERFECT!

Issue is..I dont really know where to start. I've read Randy's DIY - can get food grade SH and seem easy enough to mix with RO.

Do you dose it? I'm reading it warms up, when mixing - does it stay warm?

I mean - Kalkwasser I'm adding 24/7 - can I dose SH over a 24hr period too? Does the potency drop off, like Kalk or stay stable - to the end?

 

[Randy Holmes-Farley]

While kalk is very slightly overbalanced to too much calcium, the effect is small. At 495 ppm calcium, I’d just stick to the kalk unless there are other reasons. There’s nothing wrong with calcium running up more.

 

[vahegan]

Sodium hydroxide can be almost 1:1 replacement (in dry matter weight) to kalk: 1.6g vs 1.5g. You can calculate the amount of dry kalk matter you get dosed to your system per day if you know the volume of kalkwasser that enters the tank every day: kalk solubility in water is about 1.73g/l.
However, if you only want to slightly decrease calcium to alkalinity ratio, you can mix sodium hydroxide in your kalkwasser. Maybe reduce the amount of kalk by 5%, and mix 5% of sodium hydroxide. Note that unlike kalk sodium hydroxide is fully soluble in water (also note that it produces lots of heat when solving, and be very careful with the solution - it is very caustic).

I have been dosing two-part with solely sodium hydroxide for alkalinity in the past few months and I like the effect on the pH as well as the reaction of the system. I am now thinking of dosing 5% kalk slurry instead of two parts. Randy was suggesting against kalk slurry because it is not uniform and it may be hard to control the amount of kalk that is present in each dose. However, people have been using Jebao SLW series wave pumps to constantly mix the slurry, and I think that will keep the mixture pretty uniform - I am planning to give it a try. IMO, the only problem is if the pump fails, thick slurry from the bottom will get dosed. Those who use them tell that these pumps usually survive over a year in this mode, and they are very cheap. My concern is how to quickly detect such pump failure in order to immediately replace it. Maybe use an optical sensor on a level just above where slurry would settle: if the mix becomes transparent, then the pump is not moving water anymore. This can serve as a signal to stop dosing and sent a system alert to check the setup.

 

[Court_Appointed_Hypeman]

Sodium hydroxide can be almost 1:1 replacement (in dry matter weight) to kalk: 1.6g vs 1.5g. You can calculate the amount of dry kalk matter you get dosed to your system per day if you know the volume of kalkwasser that enters the tank every day: kalk solubility in water is about 1.73g/l.
However, if you only want to slightly decrease calcium to alkalinity ratio, you can mix sodium hydroxide in your kalkwasser. Maybe reduce the amount of kalk by 5%, and mix 5% of sodium hydroxide. Note that unlike kalk sodium hydroxide is fully soluble in water (also note that it produces lots of heat when solving, and be very careful with the solution - it is very caustic).

I have been dosing two-part with solely sodium hydroxide for alkalinity in the past few months and I like the effect on the pH as well as the reaction of the system. I am now thinking of dosing 5% kalk slurry instead of two parts. Randy was suggesting against kalk slurry because it is not uniform and it may be hard to control the amount of kalk that is present in each dose. However, people have been using Jebao SLW series wave pumps to constantly mix the slurry, and I think that will keep the mixture pretty uniform - I am planning to give it a try. IMO, the only problem is if the pump fails, thick slurry from the bottom will get dosed. Those who use them tell that these pumps usually survive over a year in this mode, and they are very cheap. My concern is how to quickly detect such pump failure in order to immediately replace it. Maybe use an optical sensor on a level just above where slurry would settle: if the mix becomes transparent, then the pump is not moving water anymore. This can serve as a signal to stop dosing and sent a system alert to check the setup.

The jebao app is pretty good at alerting with push notification on frozen pump now. I would get 2 of them just to be ready since it might freeze more often in a kalk slurry, so that way it can be hotswapped for the clean one and clean the other when convenient. Though, my jebao that gets kalk dumped right on top of it hasn't frozen yet, but given their price I still like to buy backups.

 

[DanyL]

Sodium hydroxide can be almost 1:1 replacement (in dry matter weight) to kalk: 1.6g vs 1.5g. You can calculate the amount of dry kalk matter you get dosed to your system per day if you know the volume of kalkwasser that enters the tank every day: kalk solubility in water is about 1.73g/l.
However, if you only want to slightly decrease calcium to alkalinity ratio, you can mix sodium hydroxide in your kalkwasser. Maybe reduce the amount of kalk by 5%, and mix 5% of sodium hydroxide. Note that unlike kalk sodium hydroxide is fully soluble in water (also note that it produces lots of heat when solving, and be very careful with the solution - it is very caustic).

I have been dosing two-part with solely sodium hydroxide for alkalinity in the past few months and I like the effect on the pH as well as the reaction of the system. I am now thinking of dosing 5% kalk slurry instead of two parts. Randy was suggesting against kalk slurry because it is not uniform and it may be hard to control the amount of kalk that is present in each dose. However, people have been using Jebao SLW series wave pumps to constantly mix the slurry, and I think that will keep the mixture pretty uniform - I am planning to give it a try. IMO, the only problem is if the pump fails, thick slurry from the bottom will get dosed. Those who use them tell that these pumps usually survive over a year in this mode, and they are very cheap. My concern is how to quickly detect such pump failure in order to immediately replace it. Maybe use an optical sensor on a level just above where slurry would settle: if the mix becomes transparent, then the pump is not moving water anymore. This can serve as a signal to stop dosing and sent a system alert to check the setup.

Honest question - why would you want to switch over to using kalk slurry?

I had a really long debate with myself whether to go with kalk, kalk stirrer, kalk slurry or NaOH, and after a lot of thinking I settled with NaOH because it simply made far more sense to me.

Kalk is practically insoluble.
I did the calculations and it turned out I would quite literally need a container the same size of the whole system to store kalk in the same potency as I do with 2 small containers of NaOH + CaCl2, or a daily amount which is almost double as the total amount of NaOH + CaCl2 I make for 1.5 months.

I would also need more evaporation than I currently have, and its distribution across the day would be uneven, or otherwise I would need to compromise on daily fluctuations in salinity.

A kalk stirrer does not preserve potency very well, requires weekly maintenance and outside the storage problem does not really solve anything.

A kalk slurry is messy to work with, prone to potential pump failures and inconsistency is always a concern.

NaOH solves all of this, however it does have one serious drawback - it’s dangerous and could easily leave chemical burns on your skin, which isn’t something to take lightly.

That being said - as long as you’re responsible enough and strictly follow the safety protocols of handling dangerous chemicals, accidents should not occur.

 

[vahegan]

The jebao app is pretty good at alerting with push notification on frozen pump now. I would get 2 of them just to be ready since it might freeze more often in a kalk slurry, so that way it can be hotswapped for the clean one and clean the other when convenient. Though, my jebao that gets kalk dumped right on top of it hasn't frozen yet, but given their price I still like to buy backups.

Thanks for your feedback. Yes, I have ordered the newer MOW model rather than SLW, which supports WiFi. However, I was very surprised (on another pump I have with a similar controller) that I couldn't change the operating mode or the strength using their app: only turn the pump on or off - this kinda sucks. For example, ReefOctopus WiFi controller gives full control over pump operation (but that is a different price range of course). If I can trust their pump in telling me the pump has failed, that would be some real benefit making it worth paying 50% extra for their WiFi based model (still very cheap, anyway). Yes, I am planning to by a backup pump to have it in store if the main one fails. I just want to make sure the size would be OK: I bought their smallest pump MOW-3 for use in a container that will hold about 5 liter slurry (15cm in diameter, 40cm tall). I was initially thinking of using a magnetic stirrer to mix the slurry (I have purchased huge 7.5cm and 10cm stir bars) but then have changed my mind thinking that the vortex in the bottom will not be strong enough to evenly mix the whole water column in a cylinder which is almost 3:1 in height to diameter proportion. Interesting that you dump kalk powder on the pump directly and it can stand it. Which model of the pump do you use, and what is the size/dimensions of your container? I was thinking that I would need to make a floating plate on top of the slurry (to reduce contact with air/CO2 contamination) and I could try to mount the pump on that float. My current consumption of NaOH is about 50ml/day, by using kalk slurry with concentration in a comparable range (I am using around 150g/l sodium hydroxide solution, with slurry I think I can go as high as 5-10%, will need to experiment) my 5 liters of kalk should go for quite a few months. If my alkalinity consumption goes up from my current 1dKH/day, I will use a new container, probably based on an old CaRX body...

 

[vahegan]

Honest question - why would you want to switch over to using kalk slurry?

I had a really long debate with myself whether to go with kalk, kalk stirrer, kalk slurry or NaOH, and after a lot of thinking I settled with NaOH because it simply made far more sense to me.

Kalk is practically insoluble.
I did the calculations and it turned out I would quite literally need a container the same size of the whole system to store kalk in the same potency as I do with 2 small containers of NaOH + CaCl2, or a daily amount which is almost double as the total amount of NaOH + CaCl2 I make for 1.5 months.

I would also need more evaporation than I currently have, and its distribution across the day would be uneven, or otherwise I would need to compromise on daily fluctuations in salinity.

A kalk stirrer does not preserve potency very well, requires weekly maintenance and outside the storage problem does not really solve anything.

A kalk slurry is messy to work with, prone to potential pump failures and inconsistency is always a concern.

NaOH solves all of this, however it does have one serious drawback - it’s dangerous and could easily leave chemical burns on your skin, which isn’t something to take lightly.

That being said - as long as you’re responsible enough and strictly follow the safety protocols of handling dangerous chemicals, accidents should not occur.

It is convenient to have one combined additive for both alkalinity and calcium. Also, by dosing two-part based on sodium hydroxide and calcium chloride, I am also adding a significant amount of sodium chloride to the tank, which needs to be compensated by magnesium salts and potassium/boron to maintain the ionic balance (and it will also raise the salinity which I compensate with water changes, sometimes I need to draw a bucket of saltwater from the tank and top off with RO water). Kalk slurry does not have these drawbacks and even though I can make the sodium hydroxide and calcium chloride solutions very concentrated, my 5 liter container with slurry will go a long way. I can also add magnesium and strontium hydroxide to the slurry, should I with to.

Using cheap Jebao wave pumps in the kalk container fixes the inconsistency issue and, by using slurry instead of kalkwasser, you are not tied to evaporation rate.

What I am rather concerned about, is that the high pH in the tank will probably result in increased precipitation of microelements, and whether my 5% weekly water changes will be sufficient to compensate for that. I am wondering that if I add the microelements to the slurry, would their hydroxides, that will immediately form in the slurry, eventually [partially] dissolve back in tank water? I know that CaRX proponents mention that dead coral skeletons already have all the required microelements, which is an advantage but these are getting dissolved in a much more acidic environment so I am not sure the hydroxides will work equally well. Maybe Randy can shed some light on this.

 

[Randy Holmes-Farley]

My current consumption of NaOH is about 50ml/day, by using kalk slurry with concentration in a comparable range (I am using around 150g/l sodium hydroxide solution, with slurry I think I can go as high as 5-10%, will need to experiment) my 5 liters of kalk should go for quite a few months. If my alkalinity consumption goes up from my current 1dKH/day, I will use a new container, probably based on an old CaRX body...

I do not understand how you expect to get reproducible dosing from a slurry, where the amount of solid in the cylinder declines every day.

I'm not a fan of a slurry anyway, but i think a batch process is the only way to keep the potency relatively constant.

 

[vahegan]

I do not understand how you expect to get reproducible dosing from a slurry, where the amount of solid in the cylinder declines every day.

I'm not a fan of a slurry anyway, but i think a batch process is the only way to keep the potency relatively constant.

I am not going to top off the cylinder with plain RO water as in normal kalkwasser method. When the level of slurry drops below certain mark as a result of dosing (due to constant mixing with the wave pump I expect that both solid and water will decrease simultaneously and in equal proportions), I am planning to add fixed amount of powder and water. Say, 50g of calcium hydroxide and enough RO water to make one liter, so that I always have 5% hydroxide suspension in the container.

 

[Randy Holmes-Farley]

I am not going to top off the cylinder with plain RO water as in normal kalkwasser method. When the level of slurry drops below certain mark as a result of dosing (due to constant mixing with the wave pump I expect that both solid and water will decrease simultaneously and in equal proportions), I am planning to add fixed amount of powder and water. Say, 50g of calcium hydroxide and enough RO water to make one liter, so that I always have 5% hydroxide suspension in the container.

OK, that's better than I was expecting the water replacement to be. It would be interesting to see how stable alkalinity dosing is with this method. I remain somewhat skeptical that the slurry can maintain uniformity over weeks.

 

[vahegan]

I'll report back, after I do some experimenting

 

[vahegan]

I have set up a kalk slurry reactor, and have it running for 2 days now, so far so good. I am moving from 2-parts (NaOH + CaCl2/MhCl2) to 1-part (Ca(OH)2+Mg(OH)2) dosing.
For the reactor, I am using an acrylic cylinder that was sold as flowers vase. I have mounted Jebao MOW-3 wavemaker on the bottom, so that it blows up (external magnet is under the vase bottom - had to 3D-print a support ring around the rim so that the vase sits on it and not on the magnet). I made marker marks on the cylinder every 1 liter.
Unfortunately, I didn't take photos when it was empty, now had to photoshop what it looked like:

I have mixed 4 liters of 6.5% kalk slurry (65g kalk powder per each liter of water) and added about 1.3% magnesium hydroxide to the mix.

I believe that MOW-3 (Jebao's smallest pump, it is 6@) is a little bit too small: when working on highest setting, the top layer of the slurry is starting to separate into transparent fraction if I fill above 5 liter mark (the cylinder capacity is 6 liters). I am going to order the next model MOW-5 (which is 12W) and it should be good enough for the full capacity of the cylinder. I'll keep this one as a backup pump in case the larger pump fails, and I can use it for mixing saltwater, too. They are very cheap, anyway.

Here's my reactor in operation:

The slurry is homogeneous, I have been using a strong torch from the opposite side, trying to see if there was any transparency on the upper levels, but it seems to be good when I fill to the 4 liter mark.

I tried to dose directly into the tank (similarly to sodium hydroxide) in high flow area, but it wasn't dissolving as readily and I was seeing small particles of undissolved calcium hydroxide floating in the water. I didn't like this much, therefore I drilled a small hole in the return line and inserted a 3mm acrylic pipe there, secured by epoxy. When the glue was set, I connected it to the doser using a silicone line. Now, I do not see undissolved hydroxide in the water, because of much higher flow in the pipe.

After a small adjustment of my daily dose (well, I must call it nightly dose, as I only dose at lights off to keep the pH from falling in the absence of photosynthesis), I am now seeing similar pH variations as when I was dosing sodium hydroxide. I will monitor the tank for long term effects.

P.S. I have also 3D-printed a tightly fitting lid, to minimize contamination of the slurry with CO2 in the air (even though this effect should be negligibly smaller compared with the skimmer actively mixing huge amounts of air with water). I was also thinking to maybe make a floating plate on top of the slurry, and attach the pump magnet there rather than on the tank bottom: so that it would be blowing at the bottom rather than from the bottom. I have not decided about this yet, and not sure if this approach would be any better.

 

[Randy Holmes-Farley]

I tried to dose directly into the tank (similarly to sodium hydroxide) in high flow area, but it wasn't dissolving as readily and I was seeing small particles of undissolved calcium hydroxide floating in the water. I didn't like this much, therefore I drilled a small hole in the return line and inserted a 3mm acrylic pipe there, secured by epoxy. When the glue was set, I connected it to the doser using a silicone line. Now, I do not see undissolved hydroxide in the water, because of much higher flow in the pipe.

Thanks for the update!

My concern is that in the pipe you may get significant deposits of calcium carbonate that may clog it.

 

[vahegan]

Thanks for the update!

My concern is that in the pipe you may get significant deposits of calcium carbonate that may clog it.

Thanks for raising this concern, Randy. You mean in the pipe with marine water, right? That may be possible, because it is rather small pipe, 13mm in diameter (I have a separate pump for the UV unit, the UV is not ON now, but I do not turn off the pump - so I decided to reuse the output line). It is a clear PVC pipe, and I will be regularly checking it, I am also monitoring the pH graph in the tank every day, so I will notice if there are any anomalies there.

 

[Randy Holmes-Farley]

Thanks for raising this concern, Randy. You mean in the pipe with marine water, right? That may be possible, because it is rather small pipe, 13mm in diameter (I have a separate pump for the UV unit, the UV is not ON now, but I do not turn off the pump - so I decided to reuse the output line). It is a clear PVC pipe, and I will be regularly checking it, I am also monitoring the pH graph in the tank every day, so I will notice if there are any anomalies there.

Yes, seawater plus slurry in the pipe.

Clear is good. Let us know how it looks after a while.

 

[vahegan]

My concern is that in the pipe you may get significant deposits of calcium carbonate that may clog it.

Today I noticed that the silicone tube fell into the tank and was dosing directly there. I have checked, and the small 3mm acrylic tube which I inserted into the return line was clogged, therefore the silicone tube came off due to the pressure. I cleaned the pipe with a piece of wire, but I understand, I need a larger tube, the one I used has inner diameter of around 2mm, and is too easy to clog with carbonate buildup.