I need some advice on my aquaponics system.  I have a 900 gallon system w/tilapia fingerlings and lava rock in my growbeds.  The tilapia are doing great but my pH is really high.  I have hard water and my pH is 8.2 (not very good for plants to thrive).  Do you have any suggestions for lowering my pH where I don't always have to add pH down.  I really don't want to have to add "chemicals" every day or when I have to top my totes off.  Any suggestions would be awesome.  My system has been cycling for about 3 weeks now and the pH is still very high.

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I am told that hydrochloric acid does the trick, but that's a bit caustic for my clumsy nature.  Vinegar would work, but you'll have to use more of it. 

Thanks for the reply.  I just bought some Muriatic acid (which is made up of HCl) from home depot.  I'm going to try to drop the pH by 0.2 a day until the system gets around 7.  I'll let you know if it works out.

Please keep us updated.  I didn't know of anything to say of help, but I'm curious to see how it works out.  I haven't experienced the problem myself, but maybe your experiences will teach me so I can help somebody else later on.


Hey I have about a 900 gallon tank.  I've been adding 4 ounces of muriatic acid everyday (I dilute it in a 5 gallon bucket of water).  It's been about a week or so and the pH is already down to 7.  That muriatic acid is no joke.  strong stuff

That's great, glad you got it down.  I take it the fish and plants took it in stride?  Does your ph stay down once you get it there or is there something in the system making it go up?  Right now I'm assuming that your water comes out of the tap with a high ph.

Yeah it's well water with a very high pH.  I just got it down to 7.  I will let you know if it stays at 7 or if it goes back up or down.  I'm testing the pH daily.  And the fish are fine.  All the tilapia survived but a couple gold fish died.  But thats okay. 

We don't need no stinking goldfish!  They taste like crap anyway. LOL

I talked to a guy this morning that is using lava rock as a media.  He was supposed to buy some fry and fingerlings from me but he said he checked his ph this morning and it was 8.5.  He wants to get it down before he buys the fish.  I said that was a good idea, since my ph is steady at 7.2 and the sudden ph shock could harm the fish.  He said the lava rock is supposed to be inert, but I'm wondering now since he also said he's never had ph issues before.  I hope he gets it under control since I could use the money :)

Anytime Ph is raised or lowered too quickly, even if it is acceptable you can get a fish kill.  We have some acreage of old mining pits.  Cold rain can flip the pit quickly with the water changing the PH and Oxygen content quickly. We have had thousands of fish die in this condition. Your smart to change it slowly,  You can purchase a water softener from Woods Brothers online for 400 to 600 dollars depending on the flow rates.  Carbon filtration would be even better. AP903 by Cuno 3m

Been trying to use vinegar to lower the pH of my system.  The city water here is about 8.0 - 8.2.  I read an article that when using vinegar to lower pH, it takes 1 ml of vinegar to lower the pH of 1 gallon of water by 0.3.  If that's the case, I'm going to need to add about 4.5 to 5 ml of vinegar for each gallon of top off water I add to the system.  Luckily, aquaponics systems tend to drift down in pH anyway, but I don't think that drift will be enough to keep the pH down on its own.  I'm betting that vinegar becomes very ineffective in a large system from a cost perspective.

I was looking at the Lowe's website and noticed that they have 1 gallon containers of muriatic (HCL) acid for bout $8.  Something tells me that I'd be able to use a LOT less of that to lower the pH.  I just wonder if the hardware store variety of muriatic acid will be okay to use in a food producing system.


I used this from Home Depot http://www.homedepot.com/p/Klean-Strip-1-gal-Green-Safer-Muriatic-A....  I think it's safer on the environment.  Anyways, my pH comes from the well and is in the 8's.  I have around a 900 gallon system and about one cap full of this stuff lowers my system about 0.2 a day or so.  I've heard vinegar kills the good bacteria in the aquaponics system.

Thanks Derek!  I was also looking at that bottle of muriatic acid.  If it's safer, that would be great.  According to the MSDS sheet, it's <25% HCL.  I think standard muriatic acid solution is 31-32%  A similar safer muriatic acid sold at Lowes was about 15% HCL.

Muriatic acid is safe used in small amounts and is cheaper in the long run than vinegar.  Any acid in concentrated amounts will kill the bacteria off but if you dilute it into a bucket of water before adding it to the system it shouldn't harm anything.  I add my adjusting chemicals to the sump water, so they get mixed in good there before getting to the fish tanks and beds.

Once your system is established the ph will drop on it's own down into the 6.2 to 6.4 range and you'll be trying to raise it.  Then adding a couple gallons a day to your system will help keep the ph up a little and you probably won't need to add anything to lower ph.  

My system holds about 900 gallons and I add about 30 a week to make up for evaporation and plant usage.  My system's ph is around 6.5 and my tap water's ph is about 7 so adding that amount doesn't make much of a change at all.  I add a little lime to my system every week to raise the ph to keep it in levels good for both fish and plants, somewhere around 6.6 to 6.8 is where I like it.

Good luck.


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