Gordon's Crater

Gunagulla

Ammonia now just above zero, maybe 0.1ppm, Nitrites on the way down, ~5ppm today and a big jump to 40ppm Nitrates, and pH is slowly falling, now at 7.4.
Cold rain falling into the tank this arvo and tonight, only 4mm so far, I'm hoping for a lot more, and that will no doubt cool the water a bit more.
I've cleaned all the sooty mould from the sump- that'll teach me to leave it under a White Box! I've placed it in its hole and will plumb it in as soon as I get hold of the poly fittings I need.

Pic of the system this arvo-

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BoredomIsFailure

Gunagulla wrote:

...the water returning from the GBs to the FT is slightly less alkaline than that in the tank.
This morning the FT water was at pH 7.50, but water returning from GBs was at pH 7.45.

Could it be the additional aeration? I know that when CO2 dissolves in water it creates carbonic acid, not sure if any other gasses do a similar thing. You're not dissolving any gas under pressure so it's not going to be a big effect, but then you're only seeing a slight difference.

I've noticed (and read on the forum) that tap water needs to be left to stand overnight to reach it's true pH (mine jumps from about 7.4 to around 8.3 when left to stand). I wonder if this is a similar process: gasses in solution causing a lower pH that eventually come out of solution (off-gas) when left to stand.

Hopefully someone with actual knowledge (instead of my idle speculation) will shed some light?

Gunagulla

I don't think there would be any additional CO2 dissolved in water returning from GBs, I think the strength of the H2CO3 will be fairly constant in the whole water body, since the tank water is also being aerated by the returning water from the GBs. Tap water here doesn't seem to change pH after sitting, it's always around 6, but it is rainwater with no chemical treatment.

Reticulated town water with with all sorts of additives including Chlorine and various flocculants etc would be a different matter.

BoredomIsFailure

That's fair enough - it was only a thought.

The other thing I've read is that the nitrification cycle is acidifying (the reason mature systems often need their pH buffered up). Assuming the majority of nitrifying bacteria live in the growbed, it might make sense that the water returning from them be more acidic.

I wouldn't have thought this would be measurable, but perhaps your results show that it is.

There's probably a much more obvious solution though - added anything to the media bed recently?

RupertofOZ

BoredomIsFailure wrote:

I wouldn't have thought this would be measurable, but perhaps your results show that it is.

The difference measured was negligible...

Quote:

This morning the FT water was at pH 7.50, but water returning from GBs was at pH 7.45

And I'm wondering what it was measured with.... that can distinguish to 0.05 of pH... :dontknow:

Regardless... it's not a significant difference.....

Gunagulla

Yes it was a small amount, but it was repeatable and a difference (not exactly the same every test) has been there every time I have measured over the past week or so, and that has coincided with an increasingly fast rate of change of pH, going down. Today the tank was pH 7.10. There is no doubt it is real, and I think probably due to the action of the bacteria.

I'm using an Oakton PCSTestr 35, which has claimed accuracy of 0.01pH, and I calibrate it in certified buffer solutions before use.

RupertofOZ

Yep, your pH drop is consistent with the nitrification cycle....

The difference between the pH in the tank.. and grow bed.... is probably also a reflection (as noted) of that nitrification...

Kind of kewl to actually see it measured... but of absolutely no consequence... :lol:

Gunagulla

pH 7.05
Ammonia ~0.2
Nitrite ~2-5
Nitrate 10

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Charlie

Im not sure if you know Gunner, but mint goes crazy in AP. Be carefull or it will overtake your system.

On another note, nice pic. What cam are you using?

Gunagulla

Yes, I'm aware of the crazy mint wanting to take over the GB! so I only put one cutting in the end of one bed.

Camera is a Nikon D200 and in this case, a Micro-Nikkor 105mm, earlier pics showing GBs and FT with 16mm fisheye.

ccBear

One cutting today, tomorrow the world.

Gunagulla

pH continues to fall, to 6.78 today, thats 0.6 down in 3 days, and looking like continuing, as the GB return water is at 6.69. I think I'll add a little bit of KHCO3 and shell grit to halt the drop.

Ammonia ~0.2ppm
Nitrite ~2-5ppm
Nitrate 10 ppm

Gunagulla

1 teaspoon of KHCO3 and a tablespoon of shell grit made no discernable difference, although I also added about 500l of pH6 tap water to bring the total volume up to about 4000l, which may have wiped out much of the effect. The acidity continues to rise, so time to take a bit more action I think, I'll add some Calcium Hydroxide today.

5pm 25/5 pH 6.72
9am 26/5 pH 6.52 (GB return water pH6.41)
Ammonia 0.25
Nitrite 2
Nitrate 10

At least I know the bacteria are working hard

Added 10g Ca(OH)2 @ 11:20am, which certainly had an effect:

12:05pm FT pH 6.61, GB return 6.52

Gunagulla

A slight rise in the average air temps over the past week, which has been mostly cloudy to overcast, with 7mm rain around 23/5.

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Gunagulla

Update on the Ca(OH)2 addition earlier today- the Hydroxyl ions have all been used up and the pH is on the way down again.
At 16:15 it was pH 6.52. I spread 200g more shell grit around the grow beds, mainly under the water inlets at around 3pm, when I could see it was on the way down again.

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Backyard Aquaponics
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