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Has anyone used Kalkwasser in aquaponics? It is designed specifically for use in marine applications and according to the label is is pure calcium hydroxide. calcium hydroxide is an ideal compound for raising ph due to the added benefit of raising calcium levels which are commonly deficient in systems due to the low level in fish feed. If anyone has used this stuff did you record any data on how much you added for a and how much it affected your specific system? Any input would be appreciated!

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And, I wouldn't assume your GH was ever CaCo3. Like Vlad says, test your source water and see what it says. Even if you have high KH in your source water, it may be Mg instead of Ca, as it measures the carbonate, not the divalent ion. And GH is the total multivalent ions, not nessecarily Ca

Yeah, I believe it's more of a ratio/balance situation than a saturation limit type of thing. Different plants will remove those essential elements at different paces at different phases of growth and all,...to be sure...but it really doesn't have to be all that precise...just a rough sorta balance/ratio seems to work well.Nature is quite forgiving in some ways, and this seems to be one of them. Now, one can wax poetically in tomes about "optimals"...but those are just that...optimals...hardly necessary for great growth (I'm willing to accept something growing "really, really fucking well" over "absolutely optimal" since it's much less hassle and way more laid back that way :)

Knowing the needs of your cultivar goes a long way in predicting (and proactively mitigating ahead of time) likely essential element deficiencies...things like Mg, Ca, K mostly it seems. Mg is a big one for things like brassica and cucurbits. I bet people mistake Mg def's for Fe quite often in those cases...

Ok...Cycling my new 'big' system...my source water kH started out at over 350ppm, so my pH was obviously between 8.2 and 8.5. I didn't touch it (pH or kH) for about 2 months since this is great for establishing a thriving bacterial colony and the plants (mostly lettuce seedlings) didn't seem to mind at all. I took (all in all) about 5.5-6 litres of 16-18% HCL to get that kH down to around 200ppm (this was added over a 4-5 week period of time...some to top-up water, some directly into the FT). At a kH of 180-200ppm my pH was still about 8.3. I expected as much. The adding of HCL wasn't so much to lower pH directly, but rather to lower kH thereby lessening the time it would take for bacterial respiration to be able to start lowering pH by itself. This has already started to happen.

I noticed (a couple of weeks ago) that when my kH started to drop into the neighborhood of 160-140 my pH registered at a value of about 7.8-8.0. Today my kH value is lower still...about 100, so my pH is now at about 7.3-7.5. These drops are entirely due to nitrification and not any fiddling with HCL on my part (and would probably be happening a lot faster if it weren't so damned freezing cold outside). My guess (and hence my plan) is that keeping kH at between 40-60ppm will allow me to run a nice low pH at around 5.8-6.4 while still providing enough of the inorganic carbon food source that the nitrifiers need to do their job well. At about kH 30ppm nitrification seems to be significantly (severely even) inhibited regardless of pH.

...Szwerinski et al. (1986) and Zhang and Bishop (1996) proposed ratios of one reactant to another to predict when alkalinity would become rate limiting due to mass transfer. Szwerinski proposed a predictive ratio of 3.8 grams of alkalinity as CaCO3 per gram of dissolved oxygen and/or a ratio of 12.1 grams of alkalinity as CaCO3 per gram of ammonia-nitrogen. Zhang and Bishop (1996) suggested that when the ratio of carbonate to dissolved oxygen concentration was greater than five, nitrification rates would be unaffected, and that rate limiting conditions occurred only when the ratio was less than three.
 ...These predictions are based on theoretical mass transfer limitations of HCO3-and CO2 through a thick, flat, homogenous biofilm resulting in substantial pH drops with biofilm depth (Zhang and Bishop 1996, Gujer and Boller 1986, Gullicks and Cleasby 1986, Szwerinski et al. 1986). However, nitrifying biofilms are relatively thin, 20-280 µm thick (Gullicks and Cleasby 1986, Gujer and Boller 1984, Seigrist and Gujer 1987, Boller et al. 1994, Zhang andBishop 1996). Additionally, biofilms are known to have complex tertiary structures such as cell clusters, discrete aggregates of cells, interstitial voids, and open channels connected to the bulk liquid that further decrease the maximum thickness that alkalinity (HCO3-and CO2) or other component would be diffusing through (Thorn et al. 1996, DeBeer et al. 1996). There is also evidence that ammonia-oxidizing bacteria primarily occupy the upper 20-50 µm of the biofilm, regardless of its total thickness (Schramm et al. 1996, Liu and Capdeville 1994). This is consistent with microelectrode measurements by Zhang and Bishop (1996) and Schramm et al. (1996) that show greater than ninety percent of ammonia oxidation occurring in the top 100 µm of biofilm. Zhang and Bishop (1996) saw smaller experimental pH drops across their biofilm than what was predicted by their models which assumed all 278 µm of biofilm was actively nitrifying. Consequently,mass transfer limitations of the inorganic carbon species may be much less than that assumed by diffusion based models. This is supported by the lower limiting alkalinity concentration of 40 mg/L as CaCO3 found in the Sidney Biesterfeld, Greg Farmer, Phil Russell, and Linda Figueroa Littleton/Englewood Wastewater Treatment Plant study (2001) as compared to the accepted theoretical limit of 50-100 mg/L as CaCO3.

So it seems part of why so many folks are hung up on the Holy Grail of carbonate alkalinity is (in part) due to the fact that most all the voluminousness "classic" research (and advice) on the topic is based on an incorrect diffusion model which assumes nitrification is happening throughout the entire thickness of the biofilm...thereby jacking up the theoretically needed kH numbers significantly, numbers which are stated in numerous papers, classrooms, and books on the topic.

Everything I've come across only confirms my previous statement (earlier in the thread) that there doesn't appear to be anything all that 'special' about carbonate alkalinity as opposed to non-carbonate alkalinity, other than providing a carbon (inorganic carbon) food source for our bugs.

I now understand much better where Nate is coming from and have to fly with him on this one. If you keep a tight control over the amount of carbonates in your system, (not dipping below the threshold amount which supplies our nitrifiers with the requisite carbon species food source of course), you, as the operator, are afforded a spectacular level of pH control (by the use of hydroxides). Assuming of course you have a rain water collection system or an RO system...

Thanks for that great info Vlad, I'm going to have to do some reading on the material you referenced so I can get a better understanding myself. 

I have stumbled across this post today and it got me thinking http://community.theaquaponicsource.com/forum/topics/ph-4-33?page=2.... How do you feel about the use of sulfuric acid to lower pH as opposed to HCL / muriatic acid? 

Sure, why not. I doubt the sulfates would ever really become a problem with the amounts you'd be using.

I do have to take issue with that post alluding to chloride ions becoming a problem for plants though. I mean, many aquapons salt there systems purposely for those very same chloride ions (for the fish) to the tune of 1-2ppt (yep, you read that right...parts per thousand) with no ill effects on the plants. It would take  ridiculous (un-realistic) amount of HCl to get you even close to that range. But sure, H2SO4 seems fine too. 

So what did you come up with as your source water's kH a while back?

I still need to look a lot of this stuff up while reading about chemistry so I made this cheat sheet.

Chemistry Cheat Sheet

C     - Carbon
Ca   - Calcium
Cl   - Chlorine
Cu  - Copper
Fe   - Iron
H    - Hydrogen
K    - Potassium
N    - Nitrogen
Na  - Sodium
Mg - Magnesium
Mn - Manganese
Ni  - Nichel
O   - Oxygen
P   - Phosphorus
S   - Sulfur
Z   - Zinc

GH - General hardness (a measure of the concentration of divalent metal ions such as calcium Ca2+, and magnesium Mg2+)

KH - Carbonate hardness (a measure of the alkalinity)

pH  - "power/potential of hydrogen" (A measure of the concentration of Hydrogen atoms, H+)

Alkalinity - The capacity of water for neutralizing an acid

Acid - The negative logarithm of the concentration of hydronium ions - substance that increases the concentration of hydronium ions (H3O+) in solution

Base - The positive logarithm of the concentration of hydronium ions -substance that can accept hydrogen ions or more generally, donate a pair of valence electrons. A soluble base is referred to as an alkali if it contains and releases hydroxide ions (OH−)

Ion - An atom or molecule in which the total number of electrons is not equal to the total number of protons

Anions  - Negatively charged ions

Cations - Positively charged ions

Chelate - The way ions and molecules bind metal ions to allow the metals to be available to plants as nutrients

Ligand  - That which binds to a central metal atom

Divalent - Forming two bonds with other ions or molecules

Anhydrous - Contains no water


CaCO3   - Calcium carbonate (Chalk,  agricultural lime)
CaOH2   - Calcium hydroxide (also called slaked lime, hydrated lime, pickling lime, builders lime)
NaHCO3  - Sodium bicarbonate (Baking soda)
KHCO3    - Potassium bicarbonate (an ingredient of baking powder, also used in fire extinguishers)
K2CO3     - Potassium carbonate.  (primary component of potash)
KCl          - Potassium chloride (available as water softener)
KOH        - Potassium hydroxide
K2SO4    - Potassium sulfate
HCO3      - Bicarbonate
HCL         - Hydrogen Chloride (forms Hydrochloric acid the aqueous solution of hydrogen chloride)
H2CO3  - Carbonic acid (formed by CO2 and H2O as in club soda, soda water, sparkling water, or seltzer water and acid oceans due to burning fossil fuels)
H2SO4    - Sulfuric acid (Used in acidic drain cleaner, and electrolyte in lead-acid batteries)
HNO3    - Nitric acid
H3PO4    - Phosphoric acid
CO2        - Carbon dioxide
OH−         - Hydroxide (functions as a base)

Well I have moved since then and only top off with RO water now. My source water at my old house had a pH right around 8. the KH was around 20 - 50 ppm. I got a calcium test kit and it showed approximately 150 ppm. I'm not sure if in aquaponics that is considered high or low? If we were talking about swimming pool water that would be low and that would be a good thing haha but I'm not sure in regards to aquaponics. I thought that since the pH is so high it almost always means that the KH is also going to be high? I guess that water could be the rare exception. I live in southern California and it's generally excepted that the water supply is very hard water. It is my understanding that the hardness comes from calcium and magnesium in the water. 150 ppm does not seem very high though. It pretty much stumped me and honestly I had stopped thinking about it since I moved. What do you think???

Vlad Jovanovic said:

Sure, why not. I doubt the sulfates would ever really become a problem with the amounts you'd be using.

I do have to take issue with that post alluding to chloride ions becoming a problem for plants though. I mean, many aquapons salt there systems purposely for those very same chloride ions (for the fish) to the tune of 1-2ppt (yep, you read that right...parts per thousand) with no ill effects on the plants. It would take  ridiculous (un-realistic) amount of HCl to get you even close to that range. But sure, H2SO4 seems fine too. 

So what did you come up with as your source water's kH a while back?

oh yeah and my GH was off the charts high. It took so many drops that the final color wasn't even what it was supposed to change into. It was just some dark murky color...

Benjamin said:

Well I have moved since then and only top off with RO water now. My source water at my old house had a pH right around 8. the KH was around 20 - 50 ppm. I got a calcium test kit and it showed approximately 150 ppm. I'm not sure if in aquaponics that is considered high or low? If we were talking about swimming pool water that would be low and that would be a good thing haha but I'm not sure in regards to aquaponics. I thought that since the pH is so high it almost always means that the KH is also going to be high? I guess that water could be the rare exception. I live in southern California and it's generally excepted that the water supply is very hard water. It is my understanding that the hardness comes from calcium and magnesium in the water. 150 ppm does not seem very high though. It pretty much stumped me and honestly I had stopped thinking about it since I moved. What do you think???

Vlad Jovanovic said:

Sure, why not. I doubt the sulfates would ever really become a problem with the amounts you'd be using.

I do have to take issue with that post alluding to chloride ions becoming a problem for plants though. I mean, many aquapons salt there systems purposely for those very same chloride ions (for the fish) to the tune of 1-2ppt (yep, you read that right...parts per thousand) with no ill effects on the plants. It would take  ridiculous (un-realistic) amount of HCl to get you even close to that range. But sure, H2SO4 seems fine too. 

So what did you come up with as your source water's kH a while back?

Hey Vlad, 

I got another question for you. You had said after digging a little deeper on the kH argument between Rupe and Nate you said you would have to side with Nate. But what I got from Nate's video is that it sounds like he believes you don't need any carbonates in the water at all. Whereas, you said "If you keep a tight control over the amount of carbonates in your system, (not dipping below the threshold amount which supplies our nitrifiers with the requisite carbon species food source of course), you, as the operator, are afforded a spectacular level of pH control (by the use of hydroxides)". So limiting the amount of carbonates you put into your system just gives you far better control over your pH but there is still a need for maintaining your kH at that certain threshold, somewhere around 40 ppm? Thanks

Well...hmm...yes and no. I also said that I didn't think that there was anything "magically delicious" about carbonate alkalinity...other than providing a convenient carbon species food source for the bacteria.

I'll have to re-watch that video...but Nate is in fact adding some carbonates to his system (albeit probably less than most of us) every time he adds dolomitic lime. 

Yes, "conventional wisdom" from the world of aquaria and waste water treatment studies say 40ppm is the threshold, so that would be the solid and responsible number to advise...but honestly...(and I'm probably going to regret saying this out loud, here...but) in an AP set and setting I think even that number can potentially be 'much' lower. Though how much lower and in exactly what settings. I don't really know. It would take far more sophisticated equipment (and time) than I can afford. I have the same crummy kH test kit that everyone else has, and diluting dH readings readings will only get one so far...and isn't exactly 'reliable'.

Seeing as how their is no aquaponic "industry" to speak of to fund such little research projects, and as far as I'm aware the Aquaponic Association isn't funding such a thing either...and that such knowledge couldn't possibly be of any benefit to neither the RAS industry, nor the hydroponic industry, nor the waste water treatment industry, we probably wont be finding out anytime real soon.

The issue is PH isnt stable at 40ppm.  I just talked to some one TODAY with 40ppm and a bouncing PH.  hydrates are fine if you are in a lab and can adjust all the time say twice daily but are not teh way to go in an aquaponic system where you might not see your system for a day or more + at a time. You need the ability for the water to maintain itself for a given period of time with out changing to much. if your ppm is at 40 and you have one fish die or your fan in the greeen house stops and your temps rise in your water your PH WILL CRASH and you will kill everything in your system. Can you get tight control with hydrates absolutely is it what you should use for aquaponics absolutely not. The other MAJOR reason is the fact that quite a few plants make benefit directly from absorbing carbonates into there root system. So why would  you deprive your plants of something they want and replace it with something that doesn't stabilize your water or add anything for your plants?  PH will only crash if your alkalinity is below 50ppm high or lower depending on your temp and CO2 but anything below that is dangerous and risking your entire system. You are FAR better off buffering your alkalinity up and letting that drop from an 8 to a 4 or a 10 to  6 and maintaining a stable PH than trying to hastle with keeping the KH low and hydrates high it will be far more complicated and not beneficial in any way. While hydrates work in theory they are far from the best choice when it come to practicality and actually keeping things alive and stable over the long term.

Benjamin said:

Hey Vlad, 

I got another question for you. You had said after digging a little deeper on the kH argument between Rupe and Nate you said you would have to side with Nate. But what I got from Nate's video is that it sounds like he believes you don't need any carbonates in the water at all. Whereas, you said "If you keep a tight control over the amount of carbonates in your system, (not dipping below the threshold amount which supplies our nitrifiers with the requisite carbon species food source of course), you, as the operator, are afforded a spectacular level of pH control (by the use of hydroxides)". So limiting the amount of carbonates you put into your system just gives you far better control over your pH but there is still a need for maintaining your kH at that certain threshold, somewhere around 40 ppm? Thanks

Thanks for the input Steve. I hadn't read this post in a while and forgot how much awesome info it contains. Most of which came from Vlad, so thanks Vlad you're awesome and possibly a mad scientist :) Anyway in regards to your comment I definitely agree with the part about exclusively using hydroxides doesn't allow much time away from your system. I have a system set up in my office and buffer the pH exclusively with hydroxides. I've been doing so for about 6 months. Without any carbonates in the water (except for the small amount that enter from the fill water) I'm constantly having to add either KOH or Ca(OH)2, usually every other day. It's a pretty small system (about 40 gallons of water) so it only takes a small amount but still I have to do it every other day. I have found that 1/4 tsp of KOH & 1/4 tsp of Ca(OH)2 takes my pH from 6.6 to 6.8. (approximately 7.5 OZ a year of each) In this system I have successfully grown peppers, tomatoes and about a dozen different kinds of leafy greens. I have One massive Oscar fish, an African Cichlid, an upside down cat and a Plecostomus. All of the fish are in perfect health very large. I have experimented with keeping the water temp from low 70's all the way up to mid 80's. I have even neglected the system for weeks (it happens when you have a 12 month old baby ;) and upon my return from my aquaponics hiatus I would test the water with my API master kit and would get a pH reading of 6.0. Now that is the lowest that the color chart will read but that doesn't mean that's where my water's pH was. After adding about 1 tsp of both KOH and Ca(OH)2, the pH finally came back up to about 6.6. So given my earlier data on my pH maintenance, that would put the pH somewhere down in the low 5's. 

So using hydroxides exclusively DOES mean that you will have to monitor you system more carefully than if you were "buffering" with carbonates or even a combination of the two. But for a lot of people that is a very good thing. It gives me greater control over my system. If I need to supplement some K or Ca I can do so quite freely. As far fish health goes it didn't really appear to bother my fish at all and there have been multiple occasions where I went some time neglecting my office system. I would have to hypothesize that's because the acidification of the water was gradual over a couple weeks the fish adjusted to it. I also tested NH3, NO2 and NO3 and saw no change. 

I love to see a study done on plant growth and different KH levels and a comparison of plant growth at zero carbonates and then at increasing levels. Maybe some plants are more sensitive to it than others. 

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