Backyard Aquaponics
A place to discuss aquaponics

I recently put in a data logger to log the pH changes in our system here at Challenger Tafe. The pH and water temperature were logged every hour for 36 hours. What it shows is the significant change in pH over time as the nitrification process takes place. Hence the need to renew the Carbonate and Bicarbonate Hardness on a regular basis.

Yep, that's what we've been telling people for a couple of years... nice to see some actual datalogging though...

What did you use to data log Tony???

Must admit I'm a bit surprised to see the pH vary so much over the course of a couple of days though...

What would your explaination be for the steady decline in pH value on day two, compared to day one where they rose and fell....

Rupert the pH meter is a Winlab which is a German brand. It has a data logging function built in.

As for the pH change I checked our entry sheets and the only thing I can see is that we increased the biomass i.e. added more barramundi to the system the day before. So the drop in pH may have been due to the increase in ammonia causing the nitrification process to increase and more bicarbonate being used up in the process.
Another possibility and this is a question someone mentioned that as we have one of the growbeds being blue metal this can lower the pH. Has anyone any evidence or experience that blue metal can lower the pH?

To answer this question you will need to get the rock tested. A Lot of hardrock has sulphides in it but it varies dependent on the mineralogy of the rock and this changes not only across locations but can have great variability within one location. I would not expect that bluemetal available for sale would have any significant levels as all mined hardrock must have leach tests done on it before it is allowed to be stockpiled or sold to remove the possibility of acid drainage issues.

As sulphidic rock is exposed to water and oxygen it oxidises releasing suphuric acid, commonly know as acid mine drainage (AMD) within the mining sector. Grow beds would be great for producing AMD as they are not constantly flooded but kept moist and oxygenated. Australia's biggest AMD problem at My Lyell in Tasmania is caused by 100's of thousands of tonnes of broken sulphidic rock being exposed to high rainfall that flows through the broken rock and out into the Queen River. The sulphides are not readily depleted by oxidation and oxidation will continue to occur for 1000's of years. The pH of the water exiting the mine at Mt Lyell is close to 3

Buffer that pH up ASAP tony - your heading for a major crash, all the bacteria will die very rapidly at lower pH levels.

Thanks Burnsy for that background on Bluemetal and the potential for acidification. I guess you being a former mine geologist your understanding of gravel material would be better than most. Thanks again.

Outbackozzie thanks for your comments. I started straight away buffering the system with Calcium Carbonate when I saw the initial data logging results and I'm adding some every day. The pH is around 6.2 and stable but I will slowly raise it to 6.8 over the next week. As I am running Barramundi the water temperature is 25 C which is a great help to the bacteria. By the way are you still after Barra or Black Bream later this year?

October Bream Tony

I very rarely cracked 25 deg last summer, so barra are out.

No worries Tony, just a correction though so people don't get me wrong, my background is environmental biology not rock licking (geology)