Stuppy Aquaponics Blog

pH-Alkalinity-Feed Rate Interactions in Aquaponics

Posted by Conor Quinlan on Oct 25, 2016 12:48:58 PM



Nitrogen (mg/L)






Total Ammonia




Temp (Fo)



EC (mS)










By: Conor Quinlan

Water Quality: After the weekend the water quality is still maintaining at a pH over 7. This seems like a long period of time to maintain given the still low alkalinity so therefore it is possible that a reduction in hardness is only one of the reasons why pH is maintaining. Reducing the feeding rate could be resulting in a slower nitrification rate thereby lowering the amount of acid produced over time enabling alkalinity and pH to maintain longer.


ALKALINITY AND pH AND HARDNESS AND FEEDING RATE: Originally reduced hardness from draining the aquaponics system was the reason a higher alkalinity and pH could be reached however the alkalinity and pH have been maintaining ever since; so I am hypothesizing that the reduction in feed amount from 210 grams/day to 150 grams/day on 10/7/16 is contributing to an overall decrease in the nitrification rate within the system leading to more stabilized parameters.

In other words the more waste there is to transform into plant available nutrients, the higher the nitrification rate, the more acid is produced and the faster water quality parameters change. Therefore in order to maintain water quality parameters as long as possible it is important to NOT over feed the fish in the system.

Overfeeding can also lead to the rapid accumulation of nutrients and permanent hardness as a result of CaCO3 addition which would be required to maintain pH and alkalinity at a higher feeding rate. The EC and nitrate concentrations will continuously increase if the feeding rate is too high. 

Plant Quality: All crops are doing very well given the cooler conditions. Basil seems to be developing more color since thinning them.

It is well known that aquaponics provides one of the most sustainable and non-wasteful growing methods available however with that being said the nutrient solution and solid sludge needs to be drained from the system regularly to prevent accumulation. In order to reduce the amount of runoff two large outdoor growing beds will be supplemented with the drained aquaponic nutrient solution and sludge.

Several varieties of cool season crops including, iceburg lettuce, broccoli, asparagus, artichokes, cabbage, kale and spinach will be added to the media grow beds. Using the aquaponics waste to water and fertilize the outdoor crops will further conserve resourced. The outdoor crops will be watered with drained nutrient solution and waste sludge from the aquaponics system and research will be done to determine the effects of such solutions on outdoor plant growth.

one month from seeding.jpg

Above is an image of the crops planted on 09-09-16. It has been just over a month since seeding and they all appear to be on track for proper harvest time.

one month old lettuce in NFT.jpg

Above is an image of the leafy lettuce growing in the NFT component of the system since 09/09/16.

New Information:

OUTDOOR GROW BEDS: Two outdoor grow beds that covering an area of 140 ft2 will be planted with a variety of cool season crops to observe how nutrient and sludge supplements drained from the aquaponics system will affect crop growth. This will provide a means for utilizing the waste from the aqueduct system that would otherwise be dumped.

Sludge collected from the system will be applied to the top of the grow beds where it will seep into the soil slowly over time as excess nutrient solution and low levels of tap water are applied. The media beds will need watering about 3 times per week and I will be rotating between nutrient solution and tap water.

Currently all the crops for the outdoor area have germinated and will be grown to seedling size (about 2” tall and/or wide) indoors before being transplanted to the outside. They will handle the greater variations in temperature and humidity once they have matured a little. 

seedlings for outdoor beds.jpg

Above is an image of the seedlings that are being grown for the system and the outdoor raised beds. The individuals with larger dark plugs will be transplanted outdoors.

outdoor raised beds.jpg

Above is an image of the outdoor raised beds. Each is covered with a layer of mulch.



Topics: Aquaponics, Plants, Water, Fish