Backyard Aquaponics
A place to discuss aquaponics

Does anyone know a supplier of Potassium Hydroxide in Brisbane.. I would like to use it as a ph buffer alternating with hydrated lime (the potassium would be good for my strawberry plants). Having trouble finding some in Brisbane and there are restrictions on mailing it apparently since it's use in making methamphetamines.

Could use potassium bicarbonate instead. I got some from a ag stock supplier in Perth.

Hi Matt,

Well that is sort of what I have been doing (using Eco Rose in the sump not as a spray, which is mostly Potassium Bicarbonate I believe) but then I watched on of Nate Storey's YouTube videos on buffering pH up and he was recommending staying away from carbonates (something to do with losing control of pH adjustabillity in the long term).
I could make it from ash apparently but it all seems a bit much work and would be concentrated

Nate's video is confusing in that sense... and not really true...

Potassium BiCarbonate is just fine to use as a pH buffer... especially when alternated with a Calcium buffer...

It's not going to be used in such vast quantities.. singularly.. or over time... so as to cause any loss of "control of pH adjustabillity in the long term"

Yeah. I thought he was making a rod for his back. Ok if you want to have fine control of ph and have to adjust it daily cos there is no buffering, but I would rather have a slowly moving ph that I need to buffer less frequently.

I use KOH and Ca(OH)2 on a daily basis to control my pH, plus I have quite a few kg of shell grit as a buffer. Any chemical supply company should stock KOH, I got my 5litres of 50% KOH solution from a small operator at Bendemeer (the place where the trucks stop on the way between Coffs Harbour and Tamworth to sort out any straight bananas )
I bought 5l, which is more than enough to grow out 80 trout twice- I'm only about 1/3 through the 5l, towards the end of one trout growing season.

You could try here:

Industrial Cleansers Pty Ltd
Cleaning Products & Supplies - Geebung, QLD
Unit 2a/ 424 Bilsen Rd, Geebung QLD 4034

Soap making suppliers may carry Potassium Hydroxide (you are looking for potash lye)

But as Rupe says, unless you are dealing with Liquid Limestone as your source water, you don't necessarily have to be as worried about carbonates as Nate Plays up.
(This is where my advice to pay attention to "where" and under "what circumstances" people's advice comes from. Like people who use beach sand as their buffer and live on a small pacific Island might tell you NEVER salt your system without remembering to remind you of their circumstances and source water and other inputs. Nate is in a location where rain water is generally not an option and the well water available there is extremely heavy on carbonates and if a system is being filled and topped up with local water that is not extensively RO filered and de-ionized then you really DON'T want to add any more carbonates. Where I live the available ground water is actually more variable than that since there are some portions of the aquifer that seem to be peat filtered so some people have acidic water while others have very hard water and we do get enough rain to top up with rain water at least part of the year.)

If your system is tending acidic enough to require very frequent pH adjustment with hydrated lime, and potassium bicarbonate then I wouldn't worry too much about using some carbonates since they are obviously getting used up. Probably the main reason that large commercial operations using rain water for their systems don't use carbonates for their buffering is that you often have to use a bit more of it for the same pH effect.
AND one reason many Backyarders often get into trouble is they WAY over doo it with the carbonates. Since using garden lime tends to be a bit more slow acting and often the pH crash happens with some one with a new system who doesn't really understand and maybe wasn't monitoring pH very often. They get their pH way down below what the test kit can read. Then they add a spoon full of lime and see no change so a day or two later they add a cup full, still not enough change so they add 4 cups and so on.......... Before you realize, they have put the entire bag in and the pH has slowly started to come up and it gets to the sweet spot but of course doesn't stop there and continues to rise till it is either 7.6 or 8.something which is higher than they really wanted but now that whole bag of lime is in the system with no good way to take it out to allow the pH to come down to the desired range without waiting for all that excess carbonate to dissolve. The Hydroxides are faster to affect pH so using small quantities over several days to a week people can actually see the movement of the pH and are a little less likely to cause the pH problem I described with the carbonate. Danger with the Hydroxides are they are so much faster acting that they can cause swift pH changes which can be bad for bacteria, fish and plants and handling some of them is dangerous since they are caustic.
Using the carbonates is usually considered more "organic" Finding the right balance of inputs to keep your veggies happy and your fish healthy as well as making it easy for you to keep things stable is going to be a bit different for every situation and the makeup of your source water as well as your fish food and other inputs will also affect what this combination should be.

-remembering the comment about the pacific island system using beach sand (basically crushed coral sand) as their system buffer, well they will also claim that you probably don't need to be adding potassium because in their experience, their system has plenty of potassium and adding potassium actually could cause potassium toxicity in plants so their advice to beginners was to not only NEVER add salt but not to supplement potassium. Fine if the beginners are using the same type of source water and system methods along with the same kind of beach sand as their buffer (which probably contain ample amounts of salt and potassium and many other trace elements that come from sea water, but not necessarily helpful to some one making totally different choices.-

Thanks for the responses!

I guess I should have looked into that a little deeper than just 'jumping on the bandwagon' of what I see in a video. My circumstances seem to differ substantially compared with Nate's (thanks TCLynx for pointing out his water source) since my water comes partly from rainwater and local tap water and is not high in carbonates to begin with.
I like the idea of the carbonates resulting in slower changes as that does seem safer and I tend to make small adjustments rather than large ones anyhow. I do find it hard to get the lime to dissolve in the water though.. I tend to shake it in a 2 litre juice container filled with water first to try and dissolve it but there is often little particles left.. the Eco Rose however dissolves easily but is a bit pricey, I think I will just buy some Potassium BiCarbonate since that should be cheap and as far as I understand that's what is mostly in Eco Rose anyhow.
My system tends to try and go below the 6 every week or 2 and I buffer it back up to 6.5... I do have two socks filled with crushed seashells under the water returns from the beds but perhaps I will go collect more shells again, it's a good excuse to get out in the boat

Tom this is what I used, it took my pH from 6.5 to 7.6 and has remained at 7.6 ever since.

Add it slowly a teaspoon or a tablespoon at a time and check the pH daily until it gets to where you want to be.

Someone on the forum should be able to give you a better idea on the correct dose per litre you need.

Sodium BiCarbonate is not the best buffer to add... as it raises the Sodium content level in the system...

Rupe after your post I've read up on the Sodium problems and now know why I'm lacking Magnesium in my system.

You are correct and thank you for the heads up.


Rupe here's one of the references I found.

Patricia Duncan, Ph.D.
Georgia Center for Aquaculture Development
Cooperative Extension Program, Fort Valley State University
Fort Valley, GA

In aquaculture systems usually use Sodium Bicarbonate to balance pH, but makes too much Sodium build up for plants

In aquaponics, alternate calcium hydroxide (CaOH) and potassium hydroxide (KOH)
Plants need calcium and potassium for growth

Nutrient Toxicity for Plants
When one nutrient is in toxic concentrations it causes other nutrients to be deficient due to antagonistic actions of the nutrients

Flouride and Chloride toxicity-wilting of marginal plant parts and leaf tip necrosis
Sodium toxicity- causes calcium, Magnesium and K deficiencies





Rupe even after a 90% water change a month or so back I still have the problem of plant deficiencies and how do I go about correcting the problem?

Would dosing with Calcium hydroxide and Potassium Hydroxide fix the problem? and at what doses?, or does it come down too a 100% water change or is there a better way?

Thanks for alerting and giving me an answer to my continuing plant deficiencies.

Yeah... the inter-relationship between Calcium, Potassium and Magnesium uptake can be quite fickle....

And Sodium can substitute for any of the above quite readily... causing imbalances/lockouts...

pH adjustments are best done with alternating Calcium and Potassium buffers... or even Magnesium compounds, but they're harder to source...

Thanks Rupe.

If I could get hold of Calcium hydroxide and Potassium Hydroxide what doses would I need too correct the problem and what do I look for in the way of Magnesium compounds?

pH buffers are either hydroxides, carbonates, or bicarbonates... hard to source magnesium compounds as I said..

How much buffer is required depends on your pH level and water volume...

Assuming a water volume of 1000L+...add cautiously... start with a tablespoon at a time... preferably late afternoon..

Wait until the next day.. test pH... and repeat as necessary until you get to the pH level you want...

Hydrated lime gives you Calcium doesn't it? it's not a hydroxide but it is super cheap and you can get it at any hardware/gardening store.. or at least that is what I thought?

I was planning now to alternate hydrated lime and potassium bicarbonate... does that sound like a good idea (for backyard AP purposes) Rupe?