Lowering pH in Aquaponics

Lowering pH in Aquaponics
10 Flares Twitter 0 Facebook 1 Google+ 9 StumbleUpon 0 Pin It Share 0 LinkedIn 0 Buffer 0 Email -- Reddit 0 Filament.io 10 Flares ×

Lowering pH in Aquaponics

Many beginners and intermediate aquaponic growers are often concerned about their high pH and want a quick fix to bring it down.

This post will be short and sweet because my philosophies on lowering the pH in system with high pH are relatively uncomplicated.

Lowering pH in Aquaponic Systems

If you’re thinking about using a chemical or acid to lower your pH, don’t


[Dig deeper: Why you should NEVER use lemon juice in your Aquaponics system]

Lowering pH in aquaponicsYou’re just going to make your life more costly and complicated than it needs to be.

High system pH is almost invariable caused by carbonate buildup in the system (when it’s not carbonates in the form of limestone growbed media, concrete in the fish tank, etc.).

When it is carbonate buildup in the system, your pH is being “buffered,” or maintained artificially high by the carbonate cycle of your water.  Carbonates can be a complicated subject, so I’m not going to get into them here, but the thing to remember is that carbonates have the ability to dissolve into solution, and precipitate out of solution in a way that maintains pH in a very specific high range until one day, you’re adding acid like you usually do, and your pH crashes.  Bottoms out. Drops like a rock.  When this happens this quickly in high pH systems, the first thing that happens is nitrification stops- which we all know is a very bad thing.


How to Safely Lower pH

So what are you supposed to do?  If your water isn’t that hard, you can eventually get your system nitrification to the point where your acidification from nitrification outstrips the carbonates entering your system, leading to a naturally low pH. When done correctly and slowly, the nitrifying bacteria can be given time to adjust and there’s no shock.  Once you reach this sweet spot in your system’s health and lifespan, it is a wonderful thing.  At this point you have control of your system pH.  Where do you want it? It’s completely up to you.

If your water is harder than most, or if you simply don’t want to wait, the best thing to do is install an RO filter (Reverse Osmosis).  RO filters remove almost everything from the water (including carbonates) leaving you with very pure, carbonate free water.

RO filtered water is uncomplicated stuff.  You can allow nitrification to drive pH down, or you can add simple hydroxides to raise pH (and supplement nutrients) with no long term pH effects.  RO filters can cost a few hundred dollars, but in my experience, many of the folks who spend months struggling with pH, and artificially trying to lower it, reached the point where looking back, they wish they’d just installed an RO filter and avoided the cost and heartache of fighting the fundamental chemistry of their system.

Don’t forget about Biological Surface Area

So there it is.  You have two solutions- either be patient, or drop some money on an RO filter.

If you do choose to wait, I do recommend using a growing technique that contributes lots of Biological Surface Area to the system.  This increases the potential amount of nitrifying biomass in your system as well as the resulting efficiency in nitrification.  This can lead to faster nitrification based carbonate consumption.

We use ZipGrow towers for this purpose because our media has massive Specific Surface Area (SSA) and really helps get nitrification at peak efficiency.


I hope this is helpful for you, and really commiserate with those of you who are struggling with this issue.

Controlling your system pH can be an incredibly frustrating task, but if you follow my advice, you can take the first steps towards taking control of your system and how it operates.



  1. Hello Nate:

    Want to thank you for all your informative videos and insight on hydroponics and aquaponics. I have an experimental aquaponic system that is just settling in and producing after several months of failures and frustration. Many of your videos have made it possible to lower the leaning curve and become productive, Now that it is growing and the fish are staying alive, I am thinking of expanding into a small commercial system and I have a few questions that you may be able to help me and your other fans. What permits or certifications are required to grow and sell produce and fish commercially? How does property zoning play out when developing a small commercial farm and if you are staying away from commercial feed and using duckweed, worms or black soldier fly larva, can you say that your product is organic? Or does it matter? I have a lot more questions but I will keep this short and ask more at another opportunity.


    Al Orozco

  2. I must agree with Nate that using acids on a regular basis is just not a good long term option. However, for some people starting up a brand new system. It can sometimes be appropriate to utilize acid to adjust the initial fill water and counteract the carbonates. The trick here is you must do it before you get any fish, plants or bacteria going in the system since adding acid to a high carbonate system is going to mean pH bouncing which is often bad for if not fatal to anything living in the system. Again, I do not recommend using acid on an ongoing basis and Never using acid in a system where there are fish, plants or bacteria already growing. If you have not yet gotten your RO filter and must use acid to adjust your liquid limestone top up water, do it in a separate container with aeration and make sure the pH stabilizes before you use that adjusted water to top up your system. Remember that whatever chemicals are in the acid that react with the carbonates can wind up building up in the system (for instance heavy use of hydrochloric acid or muratic acid on water heavy in calcium carbonate will replace the carbonate with chloride which could become problematic if any sodium chloride has been used to teat fish problems or used potassium chloride to boost potassium levels or if your source water is already heavy in chlorides or if you will be growing very chloride sensitive plants like perhaps strawberries.)

    If you do handle any of the stronger acids (like muratic acid) please use all appropriate safety measures like goggles, gloves, safety clothing and plenty of wash water handy to dilute any spills or splashes AND ONLY add acid to water. NEVER add water to acid (as in if it is not already diluted, you can’t add water to the jug to dilute it yourself or you risk a very dangerous explosive reaction in the acid container.)

    You are better off using source water that has less carbonates than would be needed to buffer your system pH and the easiest way to do this is collect rain water if feasible for your location/situation or as Nate says, bite the bullet and get an RO/De-ionising system and plan the budget to use and maintain it. If you made the mistake of using limestone as your gravel, get rid of it and buy new pH inert media. (To check if your media is a bad choice, take a hand full, rinse it off and drop it in a glass of vinegar, if it fizzes a lot, it is bad.)

    • What do you think about volcanic rock?

      • As long as the lava rock was not previously used for some industrial filtration process I think it would make a fine media (other than being a bit rough on the fingers.) However I doubt it will do much to lower pH long term.

    • For anyone curious, the “pH bounce” being referred to here occurs since the introduction of acidic materials does not happen instantaneously and so it takes time for the water to equalize. This is quite often why some aquaponic systems have a hard time with the pH being too low. When anything acidic, that is a lower pH than the tank or source water, then there are buffers involved to neutralize this acidic, but this process is not instantaneous. So, even though the water’s pH drops after a dosage, this does not mean the water’s pH has actually dropped. This process takes time for the buffers to counteract the pH drop and aeration’s agitation decreases this process time.

      The pH bounce is the same with di-RO water, rain water, and chemical acid such as hydrochloric acid.

      However, since acid is more concentrated, much less is required to be used, but this also means over dosing is much easier with a chemical acid, dependent on the acid’s concentration.

      Plants actually have a much higher chloride phytoxicity tolerance than what most individual’s give plant credit for tolerating. Chloride is quite beneficial to plants and is often overlooked. However, chloride is a salt that does not easily precipitate out of water so the chloride can eventually become too much if the plant’s and fish’s consumption rate of the chloride ion becomes low. Although, chloride is not the only salt build up concern in these systems.

      I would also be cautious of rain water due to potential introduction of pollution contamination from the atmosphere and the rain collection system. So, if rain water must be used, then be aware of where it is coming from and how it is being filtered after it is collected before introducing this water to the system.

      di-RO water is the best, but it can be extremely expensive dependent on the demand rate of using it and the extent of filtration required of the source water before the water enters the deionizing filter. The deionizing filter medium and waster water rejection is what makes the di-RO process quite expensive.

      Whether it is di-RO water or rain water or acid, I have always added this into my treatment tank, that could also be like an organic digestor tank, which is separate from my system, so that the water is left to agitate for a solid 12 hours so to properly equalize before dosing this water to the system.

  3. Hi Nate,

    Carbonate in the system will cause pH always high is because CO3- will absorb H+ (then release CO2 + H2O). Especially when we add too much CaOH2, it create CaCO3 that settle down and stay in the system.

    My thinking true or wrong?

    Thanks Nate.

  4. Morning Nate,
    As a newbie, discussion like this seem to be directed at older well established systems and not to the totally inexperience person just starting out. Its those first 2-3 weeks where problems arise and we have no idea what to do. My problem is also high pH but I have yet to add fish to the equation for fear they won’t be able to tolerate the wild swings in pH. I have granite grow beds with flake size pieces of limestone mixed in.. probably less than 1% total volume. For weeks I pour white vinegar into the system in an attempt to bring the pH levels below 7.5 and each morning its back up to 8.6. I’m afraid my fish will die before the ammonia and nitrates naturally drive the pH down. If the plants won’t grow above 8.5, do I just add the fish and then slowly lower the pH until natural takes it course?

  5. Nate,
    I have a deep water raft system and it is fairly new. The water is cycled but the ph level is so high (7.9 to 8.3) that my plants cannot absorb the iron and thus are not growing or producing as they should. I have wanted to wait it out but find that financially I need to find a way to have produce to sell. So I am considering adding a diffused c02 system into my heat exchanger right before my fish tank. Two things. Is this going to hurt my fish in the long run if I only run it during the day? and does anyone have suggestions on what BPS to set the pressure regulator at in order to keep it well balanced? My system has two sides. One for the nursery which houses a 400 gallon fish tank with troughs that hold about as much water. The larger facility houses 1,000 gallon fish tank and 60 foot long troughs that hold over 1500 gallons of water. It is completely cycled and doing well with this one exception.

    • Hi Monica,

      Do not add a CO2 diffuser- that would only complicate your system and only marginally impact pH. The solution is simple. Install an RO filter, even if it only accounts for 50% of your top off water, and use it to top off your system. That will actually positively impact pH in the long run. If you’re seeing iron deficiencies, please switch to FeEDDHA (will dye your water red) or FeDTPA, these forms of chelated iron are soluble at higher pH values.

      • Chris,
        Thanks for your response. I am using the chelated iron you spoke of and it does indeed color my water. I have an RO system but I do not top off very often. once a month or so. Do RO filters also take out any bacteria? So I couldn’t somehow run the entire system through it. Maybe there is something else going on besides the ph. The tomatoes seem to yellow some of them to almost white and then the whole plant is dying. The fruits stopped growing and the buds are wilting and drying up. It looks as though there are many things going on. I guess I will have to test for other things as well as iron deficiency. I know the nitrates are just fine.



  1. Lowering pH in Aquaponics - Bright Agrotech | V... - […] One of the most common questions from beginner aquaponics practitioners is about lowering pH in Aquaponics. Dr. Storey explains …
  2. Lowering pH in Aquaponics - Bright Agrotech | T... - […] One of the most common questions from beginner aquaponics practitioners is about lowering pH in Aquaponics. Dr. Storey explains …
  3. Lowering pH in Aquaponics - Bright Agrotech | A... - […] One of the most common questions from beginner aquaponics practitioners is about lowering pH in Aquaponics. Dr. Storey explains …
  4. Lowering pH in Aquaponics – Bright Agrotech – Vertical Food Blog » greennewstweets.com - […] Green News Source- Click to read full article […]
  5. The Top 4 Greenhouse Pests and How to Control Them - […] Lowering the pH of your system to about 6.0 for a week or two is a wise measure to …

Submit a Comment

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>

10 Flares Twitter 0 Facebook 1 Google+ 9 StumbleUpon 0 Pin It Share 0 LinkedIn 0 Buffer 0 Email -- Reddit 0 Filament.io 10 Flares ×