Author Topic: High gH  (Read 829 times)

mh

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High gH
« on: September 24, 2016, 10:10:17 22:10 »
OK.  First the water readings:

7 pH
2 kH
25 gH
22.4C
1.01 mS EC
5-10 NO3 mg/l (ppm)
<0.05 NH4 mg/l (ppm)
5 mg/l PO4
>6 mg/l SiO2

The problem I'm having is slow plant growth; I'd expect it to be more vigorous.  The fish are fine - ammonia & ammonium are under control.  Nitrates slightly up.  But here's where it gets weird.  The pH has been rock steady at 7 for months despite vanishingly low kH.  gH is very high.  I was wondering whether the high gH might be causing some kind of nutrient lockout for the plants but also buffering the pH somehow.  I know it's normally kH which buffers pH.  Does anyone else have experience of such an issue?

My plan is to take small amounts of water out the system & replace that (plus what is lost through evaporation & transpiration) with distilled water, over a number of weeks.  My hope is that this will gradually dilute gH until I start to see pH dropping and hopefully better plant growth. 

Titus

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Re: High gH
« Reply #1 on: September 25, 2016, 09:09:48 21:09 »
Hi
What is you water source?
titus

mh

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Re: High gH
« Reply #2 on: September 26, 2016, 10:07:42 22:07 »
Tap water.  As it comes out it's around pH 8 and 15 gH.  Over the last months I've taken to running it through a Brita filter first as I've only a small system (about 5-6l  per week of evaporation & transpiration).  The filter brings it down to pH 7 and 12 gH.

It could be that the plant growth has not been keeping up with the addition of calcium/magnesium in the source water, pure water is being lost through evaporation and both of which have lead to a gradual rise in gH over time.  I'm sure more plants would help (perhaps a calcium-hungry plant?), but they're not thriving in this water.

Titus

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Re: High gH
« Reply #3 on: September 27, 2016, 12:09:13 12:09 »
Hi
Lets break this down into component parts;
Plants;
I refer to Commercial Hydroponics by John Mason

Parsley, PH 5.5 to 6.0 Tolerant of cold temperature
Basil, Ph 5.5 to 6.0 Ideally 20 to 24C
Sage, 5.5 to 6.5 Ideally 18 to 24C
So the conditions you are creating would seem to be close to ideal.

Water. I personally would not use a Brita filter. Leave tap water to stand for 24hours to off gas the chlorine or use rain water. Your filter is lowering the PH. Is it adding acid? Or is it removing all the buffering agent in the water allowing the CO2 to the air to increase acidity?

Media. I am assuming any media you are using is PH neutral.

Fish food. This is really the only input into the system. I dont think fish flakes contain all the requirements. To top up this input I add relevant amounts of Seasol and Iron

I hope these points help
Titus

mh

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Re: High gH
« Reply #4 on: November 06, 2016, 11:12:24 23:12 »
Titus

Many thanks for the rundown.  The Brita filter has activated carbon, so it lowers kH and you end with more acidic water due to the interaction with CO2 in the air.  It was part of my effort to reduce the amount of calcium going into the system as I can't install a rainwater collector or RO system where I am.  I can mix tap, filtered & distilled water depending on how the system is doing.  Yes, the media is pH neutral (expanded clay aggregate). 

After a bit of further research (and thanks to Dr Storey for this one) I now understand that a high gH (or high levels of Ca/Mg) can interfere with, or crowd out, a plant's uptake of potassium.  The slow plant growth is probably down to potassium deficiency, partly linked to the high gH.   

The remedy I've been trying is firstly to dilute the hard water in the system using distilled water.  After a few weeks of throwing a little water from the system onto the garden and replacing it with distilled water, gH is now a slightly more normal 11.  The second strand is supplementing potassium.  At this stage, given the low kH of the water, I am using small amounts of potassium carbonate.  I plan to switch to a seaweed source as you suggest. I'm also supplementing iron.  The plants are starting to respond positively.  I'm working my way through a bit of a learning curve with all this, but thanks for the pointers.

mh

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Re: High gH
« Reply #5 on: November 21, 2017, 11:52:14 11:52 »
OK, well one year on I am pleased to report that the plants are looking much happier and are much more productive.  Reducing the gH to more normal levels and occasionally supplementing iron and potassium (with kelp meal concentrate) seemed to help - as well as taking a more active interest in the water parameters of the input water. 

What also made a huge difference was also adding a bit of volcanic rock dust into the system in the form of a small quantity of zeolite powder - plants quickly responded very positively.  Happier plants of course, also mean happier fish and nitrate readings have also gone down.