The perils of rain water

[Kobus Jooste]

I have not read the basic aquaponic guidelines that I collected during my first research efforts in 2008 for some time, but I do recall the list of water sources ideal for AP systems as ranking rain water rather low.  When you have options, it could therefore be avoided, but when your options gets eroded, well then you have to give it a bash and see what happens.  We are still in the grip of a severe drought, with all indications that if it does not rain significantly soon, our dams will be dry by August at the latest.  Before the rain stopped being reliable, and even before our municipal management thought that restricting water use MAY actually be a good idea, our tap water was dodgy at best.  Chlorine application is hit and miss, while poor infrastructure maintenance lead to dubious standards. 

 

Well (borehole over here) water would have been nice, but I live right on top of an enormous protected aquifer and am not allowed to drill into it.  Our clever municipal managers, however, do not consider putting a cemetery on top of it too much of an issue.  Before we became integrated into a larger water grid, the aquifer fed Uitenhage and we had fantastic water.  Supplying fantastic water is optional here now.  So in this drought, I have little choice but to turn to rain water.  It does still rain in Uitenhage, but as the water grid’s dams are not located here, it only helps nature and people with rain tanks.  The rain water has caused much pandemonium and anger in our little town.  Being far removed from a beach, most of the middle class houses have pools.  We may not fill them with tap water, thus most people have turned to rain.  It has had devastating results for most people that do not dose their pools with paint-stripping levels of chemicals.  A clear pool turns to a mucky mess in days after adding rain water, and most people just don’t get it.  Rain water is supposed to be perfect, right? Right!!

 

 

To recap, I added to water column diagram from a previous blog.  As you can see, you need to have a large amount of alkalinity in your set-up to deal with the effects of nitrification, respiration and plant activity.  Without this alkalinity, your pH will be vulnerable to shifts – most likely down in Aquaponics.  Pool water need to have an alkalinity of around 100 - 120 ppm.  I do not have specific references to minimum AP standards, but believe that it can be much higher than the pool levels.  In my case, stored rain water has a pH trending slightly towards the acidic range, and with a alkalinity below 20 ppm.  That combination can have disastrous effects on an AP system over time.  In the past, Alkalinity did not concern me much because most water sources that spent some time travelling through or over geological formations around here would have a decent alkalinity.  I’m at the point where I am going to go to the local quarry to fetch a chunk of limestone to toss into the system to try and deal with the prolonged effects of using rain water in my home AP system.  The alkalinity from the original fill, which was tap water, is long gone, and lime as I may, I have a depressed pH.  It used to hover around 6.5, but those days are gone.  Even if I lime my rain water tanks and add potassium in advance (topping up slowly to avoid pH shock) I still have to keep a keen eye on the system.

 

So for all of you out there eyeing off the grid rainwater systems, a word of advice.  They work beautifully, but you cannot sit back and assume that your system is mature, which can allow you to slack off on water quality monitoring.  A rainwater AP system is high maintenance, and require management tactics that is not typical of mature AP systems I have operated or studied literature of in the past.  With nutrient availability and bacterial action highly dependant on pH, you have to be vigilant and test your pH and alkalinity weekly.

[TCLynx]

Good Info, I know several people who have discovered this the hard way.  This one worth a sticky.  If using rain water, monitor and buffer and pH regularly.