pH Dropping Drastically in Dirted Tank During Cycle. Is this Normal? - The Planted Tank Forum
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post #1 of 6 (permalink) Old 09-16-2020, 02:47 PM Thread Starter
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pH Dropping Drastically in Dirted Tank During Cycle. Is this Normal?

Hey guys, Iíve got some really weird stuff going on in my first dirted 10 gallon tank which is just wrapping up cycling (started 8/10). I set this thing up with ~1 inch of 50/50 miracle grow organic potting mix and worm castings capped with 1.5 inches of eco complete. Itís heavily planted and itís been cycling for approximately 5 weeks. I thought it would have cycled more quickly due to a bag of bio rings and sponge I added to the filter from a well established tank, but Iíve been having the cycle stall out due to drastically dropping pH. Near the end of the cycle, the bacteria that convert Nitrite to nitrate have been doing fine. I never record nitrite at all, but when dosing Ammonia, it can take multiple days to get from 2 ppm to 0. Iíve done full water changes (7 gallons) with remineralized RO/DI water with a TDS of 250 ppm, KH of 4, GH of 11 and pH of 8.3 When I do that, the ammonia converts no problem in under 24 hours, but the pH drops drastically in the course of 3 days and then things begin to stall out again. Are high nitrates causing this pH drop? Or is the soil dropping my pH? Could the spider wood and Indian almond leaf drop pH from 8.3 to 5.7? I doubt it. I know the aquarium cycle lowers pH, but this seems extreme.

Hereís an example:
9/12 - I do complete water change with the remineralized water mentioned above. I then add 0.3 grams of ammonium chloride bringing ammonia in tank up to ~2 ppm.

9/13 - Ammonia = 0, Nitrite = 0, Nitrate = 20, pH = 7.5, temp = 75.6; I add 0.3 grams of ammonium chloride to bring ammonia to ~2 ppm.

9/14 - Ammonia = 0, Nitrite = 0, Nitrate = 40, pH = 7.4, temp = 76.7; I add 0.3 grams of ammonium chloride to bring ammonia to ~2 ppm.

9/15 - Ammonia = 0-0.25 (closer to 0), Nitrite = 0, Nitrate = 40, pH = 5.7, temp = 73.6. I test GH and KH to compare to the remineralized water I used. GH = 11 (unchanged) KH = 1 (so test turned yellow on the first drop meaning all my KH was pretty much consumed in 3 days).

I complete total water change (7 gallons) with same 250 TDS remineralized water. After the water change, tank pH was 7.9. I add 0.2 grams of ammonium chloride. I think my cycle is complete and Iím trying to figure out how to keep my bacteria alive and at the same time keep my pH from dropping like crazy while I order and receive my Neocaridina shrimp.

9/16 - Tank pH = 7.7 (still dropping)

Please let me know what you think. This one is beyond me. I want to keep dosing Ammonia to ensure my bacteria stay alive until I can get shrimp for the tank, but this type of huge pH swing would decimate livestock. Can anyone give me any advice here? Iím out of my depth. Iím contemplating adding a media bag of aragonite to the tank to try to raise my KH even higher and buffer my pH, but I donít want to raise the GH any higher than 11 as I donít think the shrimp would thrive in that environment. Please help!
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post #2 of 6 (permalink) Old 09-16-2020, 04:58 PM
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I am not as well versed in non-inert substrates but if I had to guess the source of your huge ph swings is that the substrate is only a month old. I will relate it to a teabag. once you put the teabag in water it will initially be very strong and release all that tea flavoring but as time goes on then it will have prolonged steeping time and be less strong. As the peat breaks down it acidifies the water but over time it will not have such an intense influence on the ph. if I missed something or could explain this better please do I'm also still learning. maybe read into how water hardness can buffer ph so it doesn't change so drastically?
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post #3 of 6 (permalink) Old 09-16-2020, 06:09 PM
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I'm sure the substrate is having an effect, but with your pH dropping from 8.3 to 7.7 I suspect your water is simply reaching an equilibrium with atmospheric CO2. To test this, add new mineralized water to a bare container, measure the pH and let it sit for 24-48 hours, and re-test the pH. If it lowers, then it is from atmospheric CO2.
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post #4 of 6 (permalink) Old 09-16-2020, 06:25 PM
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I can verify that nitrates as high as 50 ppm range will not by themselves drop ph below 6.5 as my neo shrimp tank had just that for awhile with an active substrate (stratum) and kh in the 0.5 range (using a Hanna kit).

I've used almond leaves as well and never seen a drop in kh from their typical use (not filling the tank up with leaves, lol).

My guess is the substrate. You probably have some Kh in the tank (I've found active substrates don't drop it to absolute zero) but with drop test for Kh it's tough to tell. And ph 5.7 is a pretty low number without a lot of acid going into the water column. If no co2 injection, has to be the substrate.
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post #5 of 6 (permalink) Old 09-16-2020, 06:31 PM Thread Starter
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Thanks for the replies. I've checked the remineralized water after 24 hours and after 48 hours and it's always steady at 8.3 pH. I'm guessing that some of the pH drop is from the conversion of the nitrogen cycle. I had it drop all the way down to 6.5 in my 20 gallon planted aquarium which has only eco complete with no soil substrate towards the end of the cycle and now after being established for close to a year pH has been steady at 8.0-8.1

I guess the soil is having a major effect. I'm going to attempt to add a media filter bag with some aragonite to the tank to buffer my KH/pH and see if I can get this thing to stabilize. I hope the soil doesn't keep bombing my pH. I'm sick of doing the daily ammonia additions and constant parameter testing and would like this thing to stabilize, so I can add livestock and get to a more weekly testing program. This tank is extremely time consuming right now. I also don't want to have to complete full water changes every 3 days to keep my pH high enough to not stall out the cycle. I wish I had seen something about this issue before I attempted a dirted tank. I would have just stuck with root tabs. Although, my plants have never grown even close to this well in my non-dirt tank.

Here's the tank. The dwarf Sag and Dwarf chain swords are setting out runners like crazy. It's just too bad the environment is so hostile for Neocaradinas for the time being.

Last edited by Darkblade48; 09-17-2020 at 12:59 AM. Reason: Please use the edit function for back to back posts to keep threads cleaner
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post #6 of 6 (permalink) Old 09-18-2020, 04:12 AM Thread Starter
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Update on this scenario:

Full water change (7 gallons) on 9/15/20

On 9/16 I checked pH throughout the day
9:00 am pH=7.7
3:30 pm pH=8.0
7:30 pm pH=7.9

My photo-period is between 9:00 am and 3:00 pm. My thought is that the 9:00 am reading is low because the lights have been off for a while, so the CO2 would presumably be higher and then at 3:30 pm, the plants have produced a bunch of oxygen, which would reduce CO2 and raise my pH back up. This is just a guess based off what I've read.

Nitrates =20
kH=2-3 (this is already dropping from the 4 KH in the water change water)

I add 0.2 grams of ammonium chloride

6:00 am pH=7.4
5:20 pm pH=7.9
10:00 pm pH=7.7

kH=2 (dropped again)

I add 0.2 grams of ammonium chloride

It seems like the pH buffering process from the soil substrate may be slowing down, but I'm still losing KH daily. I'm not sure how much of that kH loss is due to the nitrogen cycle with daily dosing of ammonia. I'm going to complete one more full 7 gallon water change with 250 TDS remineralized water to boost back up my kH once it all depletes, but I'm still contemplating trying a small media bag of aragonite in there to further boost the kH and more rapidly deplete the soil's buffering capacity.
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