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Aquaponics Tap Water Overflow Lesson

People who know me, will know my memory is pretty terrible. Whether that's because my mind wanders off on to the next thing or what I'm not sure. But it usually means I spend a significant proportion of the day looking for things! However, this lack of memory, in this case, came into play as I decided to top up our aquaponics system with some additional tap (hose) water. I estimate 100 litres of so had evaporated over the last few weeks, and the water temperatures were rising to high levels with the great weather we were having, so some cold tap water might help with that as well.

However, off I trotted onto my next task in hand whilst it continued to fill up, and, one thing led to another, and I completely forgot about the hose! I came back in the evening to the system overflowing - towards the vegetable patch with the overflow pipe I had put in, so at least not all the nutrients had gone to waste. The water was crystal clear and I could see the fish swimming about, but my concern was the Chlorine content of the water, and the possible swing in pH that might have resulted that could kill the fish (from what I've read you normally should do more than a 25% water change). In addition, I'm sure the beneficial bacteria wouldn't take too kindly to the Chlorine. We did a quick pH reading and it had indeed raised to 7.6 (up from 6.4 which it had previously dropped to). I can see the benefit of people talking about topping up their water using a reverse osmosis filter to keep the pH down in the first instance.

So, we've been keeping an eye on the fish, keeping the aeration up to help disperse the Chlorine, and so far we seem to have got away with it. However, it did make me think about the new aquaponics system I am getting ready, where I have two towers. Initially they were going to be interconnected, passing water between the two of them. Being from a technical background the idea of redundancy is always a useful principle to follow, and it made me think maybe I should incorporate that idea into the new system. Namely, that they should be run separately, so that if I should try and "top" one up with some hose water and make the same screw up again, only one tower would be affected. In a similar fashion, if each tower had it's own air pump and water pump, then a single pump failure would not bring the whole system down. In addition, and diseases would not be spread between the two groups of fish ...

Anyway, back to the problem in hand ... today I did some initial readings again, using some of the test kits I had obtained (in addition to the basic ones that I already had).

JBL and API Water Test Kits

The values from a few weeks ago, prior to the overflow incident to give me something to compare to were as follows:

pH, 7.4 - 7.6 (up from 6.4) **
Iron (Fe), 0 (down from < 0.02 ppm)
Calcium (Ca2+), 220ppm (as before**, which is too high and might be causing issues with Magnesium and Potassium uptake issues)
Potassium (K), < 2 ppm (down from > 15 ppm)
Magnesium (Mg), 2 ppm (down from 8-10 ppm)
GH (general hardness), > 215 ppm (as before**)
KH (carbonate hardness), > 200 ppm (up from < 35 ppm) **

** As you can see, our supplied tap water has a high pH of 7.6 (as I understand, so their pipes aren't corroded by acidic water) that is pretty hard and with lots of Calcium. In Cambridge, UK, our water hardness details are as follows (full report here:


"More than 60 per cent of homes in the UK have hard water and Cambridgeshire has some of the hardest water in the country. In total, 97% of the water supplied by Cambridge Water comes from boreholes drilled into the chalk** strata south of Cambridge. The remaining 3% comes from a greensand source to the west of our area which feeds Gamlingay and the surrounding villages." Cambridge Water

** Chalk is a soft, white, porous sedimentary carbonate rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. Ref: Wikipedia. This probably explains the very high levels of Calcium in the water supply.

To address some nutrient deficiencies I had been seeing, I had recently purchased some Canna Potassium (K20), Westlab Epsom Salts (contains Magnesium), Canna Iron (Fe) Chelate, Canna Trace, Maxicrop Seaweed Extract, and Maxicrop Seaweed Extract Plus Sequestered Iron. I had also used eggs shells and vinegar to make some Calcium (that's what's in the pot in the picture below if you were wondering), however, now that I can measure the calcium levels above, we can see that we don't need this. In fact, these high levels of Calcium probably explain the deficiency symptoms I was seeing, as Calcium competes with Potassium and Magnesium for the attention of the plant, who can't necessarily "see" the difference between the nutrients. So with these ingredients at hand, at least I could get things back into swing again and get the system back to where we were (with the exception of pH and KH).


Here is an image that shows some of the deficiency issues I was having (only showing in the Cucumber plant, the Sage and Peppers seem fine). As mentioned, probably stemming from the very high Calcium levels.


So, today I did a little more research on what kind of concentrations of the various nutrients above I should be gunning for. The two resources are primarily from and Bright Agrotech, and the values to aim for are as follows (please feel free to chirp in on the comments below if you think this need amending):

Iron (Fe), between 1 and 2 ppm ** (JBL test kit recommends 0,05 - 0,2 mg/l which I assume equates to 0.05 - 0.2 ppm)
Calcium (Ca2+), between 40 and 70 ppm
Potassium (K), between 40 and 70 ppm (JBL test kit only goes up to 10 ppm)
Magnesium (Mg), between 40 and 70 ppm (JBL test kit only goes up to 10 ppm)
Carbon Dioxide (CO2), 0 to 30 ppm
Chloride (Cl), 0 to 5000 ppm
Oxygen (O), 3 to 10 ppm
Ammonia (NH3), 0 to 2 ppm (less is best)
Nitrite (NO2-), 0 to 1 ppm (less is best)
Nitrate (NO3-), 40 to 80 ppm
Phosphate (PO4)10 and 20 ppm for light feeders (vegetative crops) and between 20 and 40 ppm for heavy feeders (tomatoes, cucumbers, etc.)
pH, 6 to 7.6 (ideally 6.2 to 6.7)
GH (general hardness), 5 to 150 ppm (confirmation needed on this)
KH (carbonate hardness), 40 to 150 ppm (confirmation needed on this)

** These values seem very high and off the chart on the JBL tests (designed for aquariums). The concentration of Iron recommended there would actually mean you wouldn't be able to see your fish at all which wouldn't make for being able to check on the health of your fish, so I won't be going over 0.2 ppm. NB I have read that Fe-EDDHA causes the water to be more red than Fe-DTPA when using water soluble Iron (more info here: and

So, to reach these levels, I added the following to the roughly 800L IBC of pure tap water:

Canna Iron (Fe), 290 ml
Canna Potassium (K2O), 70 ml (will make mildly more acidic)
Canna Trace Elements, 20 ml
Maxicrop Seaweed Extract, 10ml
Epsom Salt, 7 tablespoons
Remin Volcanic Rock Dust, 1 handful

Adding these (incrementally), gave me in the end the following values:

pH, 7.4 - 7.6
Iron (Fe), 0.2 ppm
Calcium (Ca2+), 220ppm (still too high)
Potassium (K),  > 15 ppm (just off the JBL chart, would estimate 15-20 ppm)
Magnesium (Mg), 10 ppm
GH (general hardness), > 215 ppm (probably 400 or so as off the chart)
KH (carbonate hardness), > 215 ppm

As you can see below, from the Iron we added, the water is already pretty red!


Next steps are to add some compost tea that is currently brewing in the next few days to top up some of the good bacteria that may have died off with the chlorine. I expect the pH and KH values to drop over time from experience. So after all that, I shall have to take more care when making top-ups (and will probably use rain water instead as will be more acidic). Not sure what to do about the Calcium levels at the moment, but will look into a Reverse Osmosis (RO) filter perhaps.

About the author

I am a nerd by trade, and run my own company (Webtechy Ltd) specializing in Microsoft technologies such as Azure, SharePoint and Office 365 as well as other content management systems. I also enjoy graphic design in PhotoShop and tinkering around with Arduino's and Raspberry Pi's. In my spare time I like to go to the gym, running (well, I say "enjoy"), and martial arts.

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