This roundtable was originally posted January 12, 2016.

Listen to this roundtable recording using the audio player above.

About the Upstart Farmers Roundtables

Upstart Farmers Roundtables are an informal, biweekly event. Using Google Hangouts video calling, a small group of Upstart Farmers comes together to share their experiences and learn from each other. Each week is guided by a discussion topic, with growers welcome to ask their own questions.

Roundtables are exclusively for Upstart Farmers, and recordings are only released to the Upstart Farmers Community.

Roundtable: pH

As a producer, running your system in the correct pH range can be really important for getting the best yields. In this roundtable, we discuss what pH is, what it impacts, and how to manage it properly.

pH is a measurement of acidity in your solution. It’s a negative, logarithmic base 10 scale which measures orders of magnitude in hydronium ions. Water, or H2O is neutral. H+ (hydroxide) makes things acidic and OH (hydronium) makes things basic. Together they make neutral water, or occasionally basic or acidic water.

pH mostly important in impacting nutrient availability (nutrient solubility).

Many times farmers are struggling with pH issues and they don’t even realize it. pH primarily affects:

• nutrient availability,

• nitrification efficiency,

• and fish health.

Hydroponics vs. Aquaponics

It is typically easier to manage pH in hydroponic systems. In a hydroponics system you chemically manage pH manually or by installing an auto-dosing system which manages pH for you.

In an aquaponic system, there are other major concerns in managing pH including the effects on your fish and your microbial population. You can get really good, efficient nitrification at low pH in an aquaponics system. The catch is you can’t run it low fast, because your microbes are very sensitive to pH swings. It’s important to maintain a certain range consistently and recognize that swinging pH up is not nearly as tough on your microbes as swinging pH down.

How does pH affect nutrient absorption?

All plant nutrients are soluble at a different pH range, including some that are really only soluble at higher pHs, or vice versa.

Most plant nutrients are available at a pH range of 5.3 to 6.3. Most hydroponic producers run their systems in the high 5’s. Now days, aquaponics producers are encouraged to run their systems in lower pH’s as well.

Understanding that nutrient absorption is impacted by pH swings allows us to use this to our advantage. We have had great success with implementing intentional pH swings within a certain, calculated range to encourage more broad nutrient absorption. A nice place to sit within is 5.8 to 6.2 (hydroponics). There’s a rhythm you will find in for dosing your pH. Let it swing over a small range (4/10s of a point), then swing it up or down and continue the same process. Finding this rhythm makes it a lot easier for you, and it also improves the nutrition of your plants if you’re swinging in the right range.

Imbalanced pH

What are the typical causes of imbalanced pH?

There are a lot things that can cause pH swings but the main ones are:

Hard water = high pH. This occurs when you are topping off your system with hard water. (Commonly a problem if you are drawing water from a limestone aquifer which has a lot of carbonate hardness.)

Natural plant nutrient absorption = lower pH. As plants consume certain ions, it will throw off pH of hydroponic solution and drive pH down.

Urea can really mess with pH. This usually occurs when people are using fertilizers that aren’t meant for hydroponics, which commonly have urea in them. Nitrification is an acidifying process. However, transitioning urea to ammonia is a basic process. These reactions cause your pH to shoot up and then drop down. Therefore, it is important to use hydroponic nutrients and not just regular fertilizers.

Algae can cause diurnal pH swings. When the sun is out, the algae consumes all the CO2 dissolved in the water (a weak acid) causing the pH to fly up. At night, it gets dark and algae consumes all the oxygen in the water and pumps out all the CO2 which that causes pH to swing back down.

Tip: You should only really ever be using either pH Up or pH Down, never both. Your system should trend in a single direction pretty consistently. If you have an auto-dosing system, it makes the management of this really easy. If you don’t, you just have to be really attentive.

Managing aquaponics microbe populations during tower cleanings

Power washing or sterilizing will wipe out or set back your microbial communities. However, the BSA of ZipGrow towers is so high that it will allow microbial communities to still be functional even if you dang near wipe them out.

Here’s our recommendation instead:

• Never wash the entire system at once. It’s best to pace it out to keep strong nitrification.

• You really only need to wash the media once a year if you’re growing really intense crop, otherwise we’ve had farmers (including us) go dang near 7 years without ever doing a full-on cleaning of the media. Microbial communities help decompose this at the same rate it is added.

• Regular, gentle cleanings can be done without damaging microbial populations by getting a tank of water roughly the same temperature as your aquaponics solution, pulling the media insert, dunking and shaking it in the water just briefly, and then pulling it right back into the tower. (Fun fact: that leftover muddy gunky water will start up an AP system like nobody’s business)

• The best thing to do during regular plantings is just to pull  the plant and root ball out of the media, and leave everything else.

• This is all true for both hydroponic and aquaponic systems.

Note: There are many misconceptions in hydroponics around the idea that leaving this root mass in towers leads to disease issues. This is incorrect. Disease problems are usually a result of detritus, anaerobic zones and poor system health.

Highly aerobic systems have incredibly fast decomposition which decompose this material at the same rate new material is added, making it not a problem. This is true in both hydroponic and aquaponic systems. Aquaponic systems have larger amount of buildup, but faster decomposition. Hydroponic systems have slower decomposition (just slightly), but they have less buildup. It all balances out.

Recommended (cost effective) ways to manage pH

If you’re running acidic – Potassium hydroxide (Caustic Lye) is cost effective, very basic (a little goes a long way), and you can buy it Amazon. Warning – it must be stored correctly and you should be aware that it will warm the water. If you use best practices, it’s safe and effective.

If you’re running basic – Phosphoric acid is the way to go. It’s also cost effective, comes in a liquid concentrate, and lasts a long time.

Note: Many labeled “pH Up” products are carbonate based products. We like to keep carbonates out of the system period if possible. If you’re running an RO on the front end, you’re doing that to get rid of carbonates so why would you add that back in? Be weary of these products.