Ok, one more time on KH

[John]

Apologies as I know this topic has been beaten to death but I am getting results that don't match most recommendations I find. 

My issue is one of low KH.   In my 180g indoor aquaponic system i use only pure reverse osmosis water salted to 1-2ppm.    I then add 50%  Hydrated Lime (calcium hydroxide) and 50% Potassium Hydroxide to settle the PH at 6.8.

It seems stable at this PH but drifts downward over a week or 2 which seems a bit faster than I would expect from what I've read. At which point I add a little more of the base solution to bring it back up to 6.8.     Plants are very healthy.  

GH is  125ppm ( or 7 dkh, 7 drops of test solution. ) 

KH is near 0.  (yellow on 1st drop.  but shows 40 on test strip. still low )

PH is 6.8 

TDS is 1430

temp 84F

Nitrate 5ppm

ammonia 0

nitrate 0

Ok. here's the big question:   I have read that I do not want carbonates in my system which is why I do not buffer with Calcium Bi-Carbonate.     KH does not seem to be impacted at all by my 50% each of Hydrated Lime (calcium hydroxide) and 50% Potassium Hydroxide.   So, am I buffering with the wrong materials?      If not, why is my KH not moving at all? 

Trying to follow Nate Storeys' advice along with many other forum posts and web sites.   https://www.youtube.com/watch?v=zP1rUMyklyc but am concerned about 0 KH. 

thanks!

 

[David Mitchell]

Thanks, that's an intellectual relief.

[Steve R]

Not to mention you can't raise crayfish or prawn at all in a hydrates system because the kh is needed for there exoskeleton.

[John]

Exactly what I was originally thinking David.  I was targeting zero carbonates originally due to Dr. Nate's videos.   I ended up with very low KH and rapid drops in PH due to nitrification.     

Upon reading all the great advice in this thread and watching the videos again, I think what the main point he is making is that you don't want to keep topping off a system with high ph, high carbonate water or add lots of carbonates to bring up PH.    If a system with lots of carbonates ( hard water ) is continually topped off with more hard water, the carbonates will become more and more concentrated because they do not evaporate off.     That is probably common knowledge to many but I missed that point and ended up killing off my 1st batch of tilapia.   Since most people don't use RO water, they probably have plenty of carbonates in the system and Dr. Nate is recommending not to add more chemically.  

I started over with a carbonate free system ( see my posts above ) and over the last month have stabilized my PH pretty well by adding just  little potassium bicarbonate.       I have 180 gallons and the PH  used to drop from 6.8 to 6.2-sh in a week.    I added over the course of the last few weeks less than teaspoon total of potassium bicarbonate and the PH seems to be dropping more slowly each time.     I am no expert but I am happy with this recipe.    I hope to use rain water soon but for now, RO plus additives is my only option. 

My new tilapia are growing like crazy and my plants look great so I feel good about this mix. 

[Ryan Chatterson]

I have to jump in here real quick to say that Dr Rakocy ran the UVI system for 20-30yrs using hydroxides... The longest running system with the most data collected on any system to date... He used no ph monitors/controllers and was not some "hydro guy"...he was an aquaculturist.

I ran multiple systems for several years using NO carbonate buffering sources... With excellent results.

The truth is, it depends on the design and operator of the system.

[David Mitchell]

It's good to hear various opinions on this, especially from those with direct and extensive experience.

My remaining question, however, for Dr. Storey, or for anyone who runs systems on hydroxides only is: What is your measured KH?

The point is: Were these folks just "not adding" supplemental carbonates, but actually had natural levels of carbonates in their water source; or did they truly have no carbonates at all?  I tend to think the former is true.

Without some sort of buffering capacity, it seems there is no system design (or operator skill) that would tolerate a low KH unless a continuous infusion of hydroxides was implemented, or no metabolism was occurring, or some other buffering agent was present.  Chemistry is chemistry.  

If anyone can further clarify this distinction: Do these systems truly have a KH of zero?  OR was "no supplemental carbonate added" yet with a measurable KH? And if KH was truly zero, how often did pH need to be adjusted?  

Thanks much.

[Jon Parr]

I can say for myself, that I have only ever used calcium carbonate to buffer pH up. When my pH drops below 6.0 and/or my KH drops below 50, then I hang a bag of oyster shells or limestone in the Fish tank. When it climbs above 6.8 or 100 KH, then I yank the bag out. Pretty easy and natural, and gradual. I have never used a hydroxide, primarily because I have never seen the pH fall without the KH falling as well, and early in my ventures I was advised to keep KH in the 40-100 range. If pH ever does fall with high KH (I'm not sure that's even possible), then a spoonful of ash is never hard to find.

[Alex Veidel]

So, here's a crazy question...How does one lower KH? My well water is quite high on the pH side of things, and I'm having a dickens of a time adjusting it in a 55 gallon drum before topping of my system.

I had been aerating these water barrels to, I don't know, prevent the water from stagnating or something like that...anway, turns out that getting the CO2 out of the water raises KH, which makes things a little harder to adjust....

Also, are there any acidic buffers that one could use to maintain a 6.8-7.0ish pH level?

[Jim Fisk]

FWIW I have been using wood ashes out of the GH wood stove to buffer up. I add about a cup of wood ash with the unavoidable natural bio-char into each of 5 IBC gbs at the water inlet so the bacteria have plenty of time working it over before the water hits the sump and on to the 5 FTs.

Had a trout fingerling die off due to low PH until I did this and everything has been fine ever since. Back up to 6.8 overnight and not a single loss since. I do this about once a month now. Wood ashes are one of natures natural buffers after all. Our artesian 300 ft. deep well water runs at about 7. System is mature at about 1 1/2 yrs of continuous cycling so naturally tries to go acidic. Trout both large and small are far more active and hungry now. Plants have always been happy with some Kale and Swiss Chard still producing meals at 1 1/2 yrs old. and stalks as big as your arm.

[Glenn]

Here's a crazy answer. I try to prep all make-up water the day prior to adding it into the AP stream. First I cycle new water through a open air (no sun light) particle filter for 4 hours to degas anything. Then I read pH. I have often seen a large difference between before and after readings so I go with the after reading. I want 6.5 to 7.2 and when high, I use vinegar and or lemon zest (not juice) small doses over time, usually no more than 2 hours while still circulating but not through the filters... After I'm satisfied with the pH I count on the normal bacteria processes in the AP to continue to act in favor of the acid balance and the minerals in favor of the basic, then it's on to more filtration, ozone purification, and normalizing/mineralization. Dadgum being a farmer is fun huh.

Alex Veidel said:

So, here's a crazy question...How does one lower KH? My well water is quite high on the pH side of things, and I'm having a dickens of a time adjusting it in a 55 gallon drum before topping of my system.

I had been aerating these water barrels to, I don't know, prevent the water from stagnating or something like that...anway, turns out that getting the CO2 out of the water raises KH, which makes things a little harder to adjust....

Also, are there any acidic buffers that one could use to maintain a 6.8-7.0ish pH level?

[Jim Fisk]

I use a small ozone gen on one of the empty FTs via the bubbler line. About as controversial as CS on here but I use both and have a healthy system. So I will stick with them. When I find my ultraviolet pond light I will try that on any algae blooms should I ever get one again now that the system has settled in.

[Vlad Jovanovic]

Hey Alex, you lower kh the same way you would lower carbonate alkalinity (the two are hopelessly interconnected, so much so that they are often considered the same thing) and how would lower pH (pH and kh also share a corollary relationship)...that is to say with an acid.

...and you should let the carbonic acid (H2CO3) off gas from your tap water (in the form of CO2). It's the only way you'll ever be able to take a realistic pH reading, so that you know what you are dealing with.

Alex Veidel said:

So, here's a crazy question...How does one lower KH? My well water is quite high on the pH side of things, and I'm having a dickens of a time adjusting it in a 55 gallon drum before topping of my system.

I had been aerating these water barrels to, I don't know, prevent the water from stagnating or something like that...anway, turns out that getting the CO2 out of the water raises KH, which makes things a little harder to adjust....

Also, are there any acidic buffers that one could use to maintain a 6.8-7.0ish pH level?

[Alex Veidel]

Thanks, good to know. I was just getting a little confused with how much muriatic acid it was taking to make an adjustment....not that I was using a lot, just seemed like more than should be necessary to adjust 55 gallons of water.

Btw, any concerns with using muriatic acid that I should know about? I'm diluting it into 55 gallons long before I add it to my system.

And if there's something better or easier I could be using to make adjustments, that would be cool to know about too :)

Vlad Jovanovic said:

Hey Alex, you lower kh the same way you would lower carbonate alkalinity (the two are hopelessly interconnected, so much so that they are often considered the same thing) and how would lower pH (pH and kh also share a corollary relationship)...that is to say with an acid.

...and you should let the carbonic acid (H2CO3) off gas from your tap water (in the form of CO2). It's the only way you'll ever be able to take a realistic pH reading, so that you know what you are dealing with.