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 Post subject: Re: Gordon's Crater
PostPosted: May 27th, '13, 14:58 
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Today's chemistry experiment: Adding Ca(OH)2 to the system, currently with ~4000litres of water.
Don't add this much in one go if you have fish!

13:40: FT pH 6.25, GB return 6.17 Amm 0.5, Nitrite <2, Nitrate 10

15:00: FT pH 6.23 then added 30g Ca(OH)2

16:00: FT pH 6.93, GB return 6.47. @ end of 20min drain. System clearly not back to equilibrium, ie not fully mixed

16:20: FT pH 6.90, GB return 6.55. @ end of 20min pump. Better mixed, but still a way to go.

In an effort to keep the water temp a bit higher than it otherwise might be, I've cut the night time floods way back, and also started heating, just using about 20m of 25mm poly pipe laying on the ground for now, the circulation pump comes on when the water pump operates, but only between 8am and 3:30pm, when the sun goes behind the hill.

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 Post subject: Re: Gordon's Crater
PostPosted: May 28th, '13, 06:39 
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Update on the effect on pH of adding 30g of Ca(OH)2 yesterday afternoon:

27/5 22:15 FT pH 6.57 GB return pH 6.34
28/5 8:15 FT pH 6.25 GB return pH 6.15

The FT-GB difference is back to normal, so I consider that the Ca(OH)2 is probably all dissolved and mixed now. There wasn't any variation between mid and edge areas of the FT either, unlike yesterday when some >pH 1 variations were observed.
Acidity is back to where it was yesterday morning, so all the added OH- ions have been neutralised by the H+ ions from the biological activity.

I'd like to get the pH back closer to neutral, so I'll add a lot more shell grit today, plus some KHCO3 and monitor the results.

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 Post subject: Media fill factor = 0.7
PostPosted: May 28th, '13, 08:29 
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I have measured the fill factor of the media in my nominal 500litre growbeds- it takes a fraction under 600litres of water from the FT to fill 4 grow beds, which shows that the 135litres of Canna cay balls + ~365litres of river gravel occupy 70% of the volume, leaving 30% for the water/air during the F&D cycle. This appears to be a fair way off the 40-50% space between the media I have seen others write about.

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 Post subject: Re: Gordon's Crater
PostPosted: May 28th, '13, 08:41 
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Yea I usually say 40% but its still only a guideline. I think 40% was adapted to give a margin of error, usually members want to know how much water they will loose from the FT on the fill cycle... so 40% is a safer number.

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PostPosted: May 29th, '13, 06:12 
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As expected, the pH dropped below 6.0 overnight, at 7:15 this morning:
FT pH 5.95 GB return pH 5.85

I don't know how much lower it will go if I dont add some more alkali or buffers, but I reckon I could throw in a few chunks of Potassium metal to halt the decrease, and get a Hydrogen gas explosion as a bonus :twisted:

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 Post subject: Re: Gordon's Crater
PostPosted: May 29th, '13, 11:07 
Grab some hydrated lime (CaOH)... cheap as chips.... bring your pH back to 6.8... or even 7.0..

You've got no fish at the moment... but will have shortly.... and below 6.0... the nitrifying bacterial colony can collapse rapidly....

No more "ammonia" additives...


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 Post subject: Re: Gordon's Crater
PostPosted: May 29th, '13, 12:00 
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Yea, I have already stopped the pee ponics action yesterday as Ammonia was on the way up again ;)

I checked the water at 11:30: FT pH 5.95, GB return pH 5.91. Measuring both lots of water did turn out to have a use, the FT water hadn't changed in nearly 4 hours, and the GB return had risen slightly, so it looks like it wasn't going to drop much more anyway. I reckon it would hit have the bottom between pH 5.9 and 5.95.

I was worried about my bacteria though, so I mixed 50g of Ca(OH)2 in water and spread that around the system at midday, and at 12:35 I was at:

FT pH 7.38 GB return pH 6.55

I'll see how it looks again later, but I reckon it wont be too much below pH7 by tomorrow.

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 Post subject: Re: Gordon's Crater
PostPosted: May 29th, '13, 15:49 
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hmmm, it looks like I still have far too many H+ ions in my water, at 17:10:
FT pH 6.49, GB return pH 6.22

I'm hoping SWMBO can pick up some KOH from the chemist this evening, otherwise another 50g of Ca(OH)2 will be going in tomorrow. I have about 120kg of it, so wont be running out any time soon!

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 Post subject: Re: Gordon's Crater
PostPosted: May 30th, '13, 08:01 
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:oops: :oops: :oops: hope I didn't kill too may bacteria with the ~half hour spike to pH10!

100g Ca(OH)2 in one go would appear to be a bit too much!

7:30 FT pH 6.05, GB return pH 5.94
8:00 Added 100g Ca(OH)2 dissolved in water
8:30 FT pH 10.2 :boggle:
Added ~1000l pH 6 tank water and ~1litre vinegar, turned the pump off for about 30 mins and added tap water to GBs
~9:00 FT pH 9.4
9:15 FT pH 7.88, GB return pH 7.65 & dropping quickly, ST 8.68
9:45 FT pH 7.73, GB return pH 7.23 8)

Strange how 100g Ca(OH)2 had a so much larger effect than 50g yesterday, when all the extra OH- ions were gone within 24h, with no huge +pH spike. Anyway, I have about 1000l of fairly alkaline water in the sump tank (pump not in there yet) I can slowly mix back in when needed.

Update
10:45 FT pH 7.34, GB return pH 6.95

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 Post subject: Re: Gordon's Crater
PostPosted: May 30th, '13, 09:49 
pH isn't linear.... it's logarithmic....

Twice as much buffer wont mean twice the pH change.... :D

And the true pH level wont be readable until at least 12-24 hours after addition...

I'd suggest that you refrain from any more chemistry experiments with fish arriving soon... :wink:


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 Post subject: Re: Gordon's Crater
PostPosted: May 30th, '13, 10:21 
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Yes, I know the pH wont settle to its true value for quite a while, but the FT-GB return difference is giving me a good indication of how it is settling back to that value.

I'm going to test it again shortly when I collect my other test samples for today, but I reckon it was probably not too far off the correct amount to add to get back up to near neutral- that sort of quantity just needs to be added over a period of hours, rather than 10 minutes ;)
However, action needed to be taken, with the pH heading back into the 5s this morning!

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 Post subject: Re: Gordon's Crater
PostPosted: May 30th, '13, 13:33 
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RupertofOZ wrote:
pH isn't linear.... it's logarithmic....


Indeed, its already back down to pH 6.58 in the FT, tomorrow I better add 1kg! :laughing3:

If I was using strips, ie not much better than litmus paper, I would have completely missed the big pH spike- even the API master test kit would mostly miss it, if you happened to test it frequently enough.

My wife forgot about getting the KOH from the chemist, so Ca(OH)2 is all I have to use as far as alkalis go, as I dont really want to be dumping NaOH in there, so I might whack in a pile of shell grit, 250g of that had no noticeable effect, so 1kg should be fine... but in the meantime I have about 1000l of pH 8.41 (currently, but very slowly decreasing due to bacteria in the water) [1] water in the sump that I will mix back in, maybe tomorrow.


[1] This has been a good demonstration that most of the bacteria live in the GB media, and not many are swimming around in the water: FT+GB pH rapidly decreasing, GB return water significantly lower than FT, and a very slow pH decrease of the ST water which is isolated from GBs.

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 Post subject: Re: Gordon's Crater
PostPosted: May 30th, '13, 13:52 
Gunagulla wrote:
but in the meantime I have about 1000l of pH 8.41 (currently, but very slowly decreasing due to bacteria in the water) [1] water in the sump that I will mix back in, maybe tomorrow.

Why do you want to mix 1000L of water at pH 8.4... into your system...

You said you were going to add more shell grit.... so let things stabilise...

You wont be able to move pH around by more than 0.4... at any one time... once you have fish in there....


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 Post subject: Re: Gordon's Crater
PostPosted: May 30th, '13, 14:20 
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I want to mix it in because the FT water might be down around pH 6 again tomorrow. So far the shell grit has had no noticeable effect. The reason I'm doing all this now is because there are no fish in yet, and I am sure that fish probably wouldn't have survived, or at least been badly affected by, this morning's pH excursions! Before the fish arrive is the time to see how the system behaves as a result of various treatments I think. But yes I agree, its getting close to the time where I need to have it all stabilised.

at 15:15: FT pH 6.58, GB return pH 6.37, ST pH 8.41

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 Post subject: Re: Gordon's Crater
PostPosted: May 31st, '13, 06:39 
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8:00 FT pH 6.23, GB return pH 6.07, ST 7.18

At least the fall in pH has slowed somewhat... but then I haven't added any "bacteria food" for few days.

Time to mix some of the isolated ST water back in methinks, along with some more shell grit into the GBs

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