Testing for Alkalinity/Carbonate Hardness (KH) in Aquaponics

This is part of a series on Aquaponic Water Testing.


Alkalinity, along with CO2 levels, drives the pH level in aquaponics systems. Alkalinity is also required for the wee little beasties that convert ammonia to nitrite and nitrate. That means that maintaining the proper type and level of alkalinity is very important.

At a minimum, you would want an alkalinity of 20, or 1.5dKH.  Alkalinities can range upwards of 300-400ppm, as long as the proper type of alkalinity is maintained.

There are two types of Alkalinity, Carbonate  & Bicarbonate . Add them together and you have Total Alkalinity. As long as your system pH is under 8.3, you only have Bicarbonate Alkalinity, which is good. Bicarbonate alkalinity actually struggles to bring the pH up to 7.8. That is why I recommend never using Hydroxides, and only using Calcium Carbonate, never Potassium Carbonate.

Alkalinity is pretty easy to check. I use both the API KH test kit, and the Hanna Checker HI775. The geek in me enjoys the ppm resolution of the Hanna Checker, the miser in me knows the API test costs 1/15 the amount:

  1. API GH and KH Test Kit 1dKH resolution = 17.86ppm resolution
    $5.39
    Number of tests depends on your KH and GH levels, so cost per test varies
  2. Hanna Checker HI775 (0-500ppm range; 1ppm resolution)
    $49 / 25 = $1.96ea (@Test Equipment Depot)
    Refills $19 / 25 = $0.76 ea
  3. Hach Digital Titrator +8203
    $159@Hach + $66.95@Hach / 100 = $0.67ea
    Hach Digital TItrator+Alkalinity Reagent Set
  4. Lamotte Smart3 + 4318J (10-200ppm)
    $37.00@GlobalWater / 100 = $0.37
    Lamotte Smart 3 + Lamotte_UDV
  5. Hach DR900 + 8030 (0.05 – 4.00)
    $65.95@Hach / 100 = $0.66ea
    HachDR900 + Hardness (Calcium) Reagent Set, LR
  6. YSI 9500 + AlkaPhot (10-500ppm)
    $30.45 / 50 = $0.61ea OR $64.38 / 250 = $0.26

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