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I'm curious as to what people use to adjust the pH levels in their aquaponics systems?

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HI we were having the same problems with PH  we tried everything.  Then we ran across someone using driftwood. by harvesting some from a lakeside or river cut it up to a length you like and put it in your tank with your fish.  The fish love it and believe it or not it lowers the PH.  We also find out that you can get sorgum moss from Lowe's, Home Depot and...put some in nylon socks, hang onto the return water to the tank and it will filter thru and lower your PH.  Good luck  Mary

Vlad, what kind of wood ash do you use to make lye?  I've read hardwoods are best, but why cant I use pine? Have you ever made lye with pine ashes?


pine ash lye is much lower quality.  the pH will typically be lower and may not soponify fats as well.  for use in AP systems it may be usable however- the quality will be really variable.  

What Nate said :)

I've never tried using pine or other soft wood, I was told as a child that "it's no good" and just kind of left it at that, and everything I've ever heard/read specified hard wood ashes as well. That saying that softwood lye will only produce soft soap, may be true, or maybe one of my grandmothers "old wives tales", IDK. I have never tried. Ashes from kelp, I am told, make the hardest bars of soap.

In an AP system though I'd still probably avoid using driftwood that again came from a softwood (particularly pine) tree, as the pitch that would tend to ooze out over time could potentially cause problems for the fish. Whereas (I believe at least) the pitch from a good (especially aged) hardwood/driftwood would be insignificant...Again this just seems intuitive. It's not something I've either done or even researched much. Maybe one of the 'rocket scientist' folks (you know who you are :) could  confirm or deny this?

Hi Mary,

Driftwood, peat and sorghum can lower it a bit. It's very subtle (tannic acids if I remember) but most folks looking to bring their pH down need a little more kick. As TC mentioned previously, a mature system should start moving in that direction on it's own.

I'm actually replying because of the driftwood recommendation - fish do love it because it can really make it tough to catch them. :)

I have only purchased one product to lower pH, but I've not tried it yet. It's a pH Down product from the hydro shop in Bangkok - I believe it's Nitric Acid.

Thanks Nate & Vlad,

How would I be able to determine the quality of my lye before using it?  Would the egg in the egg test not float the same? I have a small indoor aquaponics garden and would love to try the lye thing.  It only has gold fish in it, so not a big loss if something goes wrong.  Perhaps I should check for a 'lye thread'.... :-)

Hi Katie,

KOH is available through many sources - try googling it. It comes in several grades, including a food grade. Soap making supply shops would carry it as well. It's very strong and caustic, but might not be as fun as making your own.

Thanks Chip  and indeed, would love to make my own, esp since I have plenty of ash from my stove :-)

That's a good question Kate...Nobody seemed to really know how, so this is the best that I could come up with...

But for soap, yes you could just use the egg test, or you could let the water evaporate from your solution, and just measure out the crystals with a quality scale (one that measure to the hundredth of a gram, say).  You don't want the egg to break the surface, nor do you want it to sink. It should just hover a little under the surface of your solution.

For AP you can use the formula in the blog to roughly sort of determine how many grams of KOH your solution will contain, so that you don't over do it from the get go, and have a rough idea of what it'll do before you even test it.

Then get a gallon/litre (or whatever) bucket of system water, test the pH, add a given amount of your lye, test pH again and extrapolate how much you'd need for your system from there. Keeping in mind that you really don't want to move the pH more than 0.2 points or so in a day or two (or longer even), if you care about your fish. So add less than you think you would need and test... Test again if you need... And test once more to repeat your results :)

You could even keep (and label) that test water for later use (depending on if you can figure out how much of it will effect your systems pH in a desirable way). 

If you make a "big"-ish batch of lye you can keep it for later and not have to re-test the strength.

I hope this made sense :)

I too have lots of ashes from my stove (and luckily in this case tons of hardwood trees on my property) I've begun saving them in a huge barrel, along with ALOT of humonia (in different barrels of course :) .My hope is to run side by side fertigation comparisons in one of my fields/garden this spring/summer. Using mineral salts on the one hand, and a hummonia lye solution on the other. So until then, I may or may not work out a better way to know exactly (or at least close enough) how much K is in a given solution? So far with the 'organic-hydro' the above process has worked just fine for me.   

It may not be a very "scientific" answer, I know, but it is still much much better than just straight out guessing how strong your solution is..

Try it out, keep notes, and please let us know how it goes. I'm sure others would like to create as many of there own inputs as they can,  if they know that they are doing so in an effective and safe (for their systems) way.

It's not as cool as making all your own fish food, but no where near as laborious either :)

Katie D said:

Thanks Nate & Vlad,

How would I be able to determine the quality of my lye before using it?  Would the egg in the egg test not float the same? I have a small indoor aquaponics garden and would love to try the lye thing.  It only has gold fish in it, so not a big loss if something goes wrong.  Perhaps I should check for a 'lye thread'.... :-)

Thanks so much for all the great information!  I'm going to try this soon and let you know how it goes.  Its not that I have problems with the pH in my tank, just would love to find a more natural way when I do adjust it (using just regular 'pH Down' for now).  Plus it'll give me something to do with all the ash.  Also read that putting the leeched ashes on gardens is great.

Wish there was some way to 'thumb up/thank' people for their posts...

Wait. Did you mean pH UP?

Lye will bring your pH up (more alkaline) not down (more acidic). Just want to make sure that that was a typo on your part?

Doesn't your AP system naturally tend to go more acidic over time? (falling pH that needs to be buffered back UP)

Driftwood (not ashes, but an actual piece of wood) in water will bring pH down as it releases tannic acid, thereby acting as a sort of natrual pH Down product. 

oops ya, I was just making the point that I use the store bought stuff from a hydro store.  I have other hydroponic systems and use the 'down', the bottle is sitting in front of me, probably why I thought of that first.  I rarely have to adjust the pH in my aquaponics system, and usually can do so just by adding more water.  The lye would be very useful in another grow bed that I am having major pH issues with (but that's not an aquaponic setup, probably why I'm having probs). 

Thanks for checking though, would be a frustrating mistake for someone expecting the opposite results...

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