Why is pH stuck at 6.6-6.8 in a cycling tank with Amazonia - The Planted Tank Forum
 
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post #1 of 6 (permalink) Old 05-19-2018, 03:41 AM Thread Starter
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Why is pH stuck at 6.6-6.8 in a cycling tank with Amazonia

I'm currently cycling 20 gallons long with 9L of Amazonia Light and 3L of Amazonia. I am using brita water while it cycles and ever since I got the water in, the pH is sitting around 6.6-6.8.

My understanding with using tap water active substrates was that it affects how long the buffering capacity will last for due to KH, but will not affect how low the water will be buffered to. But KH in this tank was stripped completely after day 1 and for over a week, the pH is staying higher than expected (low 6 to high 5s).

So does anyone know what mechanism is causing my pH is not dropping as low as it should with Amazonia?


Just to clarify few potential questions, tank only has amazonia, dragon stone, sponge filter and monte carlo.
Brita parameter: pH 7.2, KH 3-4. GH 5-6, TDS 115.

Thanks in advance!
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post #2 of 6 (permalink) Old 05-19-2018, 06:39 AM
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In the first paragraph you say pH is 6.6 - 6.8 but in the second paragraph you say pH is low 6 to high 5. And I am assuming you are using a digital pH meter.

From Brita to tank you got about 0.5 pH drop and no kH left. Not bad.

With no acid coming in, how do you expect the pH to drop farther? If the tank is still cycling, then you still have ammonia, which is base. Once the tank cycles, you will probably get another 0.1 - 0.2 drop.

If you need to go lower then you need to find an acid source, where injected co2 + h2o might be one.

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post #3 of 6 (permalink) Old 05-19-2018, 12:36 PM
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What pH range are you trying to achieve? I was under the impression that ADA soil usually buffers pH to around 6.5, give or take. Being as you aren't using RODI, this effect won't last but so long anyways. The substrate can't bind with but so much KH before it becomes exhausted. As OVT mentioned, you'll need some form of acid to get it any lower, whether it be tannic acid from driftwood, peat, IAL, etc. or carbonic acid from dissolved CO2. You'll also want to stop using "filtered" tap water if you want the pH to stay in the lower range for any significant length of time.
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post #4 of 6 (permalink) Old 05-21-2018, 03:15 AM Thread Starter
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Thank you guys for the input!

Quote:
Originally Posted by OVT View Post
In the first paragraph you say pH is 6.6 - 6.8 but in the second paragraph you say pH is low 6 to high 5. And I am assuming you are using a digital pH meter.

From Brita to tank you got about 0.5 pH drop and no kH left. Not bad.

With no acid coming in, how do you expect the pH to drop farther? If the tank is still cycling, then you still have ammonia, which is base. Once the tank cycles, you will probably get another 0.1 - 0.2 drop.

If you need to go lower then you need to find an acid source, where injected co2 + h2o might be one.
Yes I do. Calibration goes out of wack sometimes but it should have been correct since I double checked with drop tester.

High 5s to low 6s was my expectation of pH drop from reading other's experience with using active substrate for buffering (for shrimp tank). As far as I know, Amazonia has humic acid being released which is why pH drops.

I don't use CO2 on tanks with shrimps, so I guess I'll try alder cones or IAL. I just wanted to know if there was a reason for why my tank is stabilizing at 6.8 when I see Amazonia buffering down to quite a low pH in some cases.

Good thinking with ammonia, it didn't occur to me. I still have about 0.25-0.5 on drop test showing up although I'm not sure how much effect on pH that'll have.

Quote:
Originally Posted by madcrafted View Post
What pH range are you trying to achieve? I was under the impression that ADA soil usually buffers pH to around 6.5, give or take. Being as you aren't using RODI, this effect won't last but so long anyways. The substrate can't bind with but so much KH before it becomes exhausted. As OVT mentioned, you'll need some form of acid to get it any lower, whether it be tannic acid from driftwood, peat, IAL, etc. or carbonic acid from dissolved CO2. You'll also want to stop using "filtered" tap water if you want the pH to stay in the lower range for any significant length of time.
Trying to achieve low 6s, that's desirable for Taiwan Bees that I'm going to be keeping. I just moved so my RO unit didn't have high enough flowrate to refill my other tanks. Figured using tap wasn't going to hurt for initial flooding as I change soils out pretty regularly, but yea I'm going to be using remineralized RO. And I brita'd the tap to lower KH by I think around 1-2 KH.

Oh, I thought the expected buffered pH was high 5s to low 6s as it's recommended for TB tank which is kept in that pH range. Also, another tank I have set up (with RO and just regular Amazonia) is consistently buffered around 6.0-6.1.

Any idea on anything to use for acid buffering that doesn't use tannic acid, besides CO2 injection? Don't like the brown water look too much and prefer to go the other route if I can.
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post #5 of 6 (permalink) Old 05-21-2018, 03:31 AM
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White vinegar, as I saw some references to it?
I would certainly research it more before using.
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post #6 of 6 (permalink) Old 05-21-2018, 03:38 AM Thread Starter
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Update: Okay looks like pH just crept up past 6.8, it's going up towards 7 now, pretty sure I didn't exhaust the soil that quickly lol. Here's my record of pH:
10 - 6.82
11 - 7.18 (This is probably because Brita water comes out around 6.8 and creeps up to 7.2 after aging)
14 - 6.83
15 - 6.80
16 - 6.62
17 - 6.57
18 - 6.63
19 - 6.74
20 - 6.92

Interesting, looks like I'm going to have to find other ways of lowering pH is it stays this way after cycling and change to remineralized RO.

Bump: Vinegar sounds accessible, I'll do more research to see if it can be reliable and consistent. TBs are pretty sensitive to change and expensive too lol.
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