How Quickly Can You Drop Ph Without Hurting The Fish?

evangemeren

Junior Poster
Oct 5, 2013
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Thank you so much to all of you who frequently post here. I've learned so much from reading your questions and posted answers.

I'm unclear on one key detail: how quickly can you drop the pH in the tank (to achieve the required CO2 concentration) while still keeping the inhabitants safe?

Background:
  • I've got a 130 gal. "high tech" planted tank (high lighting, CO2) with Ultum Nature Controsoil (buffers the water) and several large pieces of Malaysian driftwood.
  • I run it with a 40 gal. sump in the stand so I can keep all of the equipment hidden from sight.
  • The tap water in my area is basically liquid rock ... so instead I use RODI water that I remineralize to 4 dKH using Aquavitro Carbonate, and to 4 dGH using Aquavitro Mineralize and Seachem Discuss Trace
  • The new water has a pH of around 7.8 to 7.9 before being added to the tank
  • I use an Apex controller to monitor the pH of the water flowing through the sump, and cycle the CO2 solenoid to maintain the pH around 6.7 (see control chart from my Apex ... orange trace is pH, blue bars are when CO2 is on)
    pH and CO2.jpeg
  • I have Discuss in the tank, along with a few bushynose Plecos, Rainbow fish, Siamese Algae Eaters, Greman Blue Rams, and Tetras
  • The tank is quite heavily planted with several slow-growing species of Anubias, Buce, and Amazon Swords
  • In case it is relevant, the tank stays at 82 degrees F.
  • I perform a 25% water change every 3 days (I am always worried about water quality for the Discus, and like seeing crystal-clear water).
  • I fertilize using Aquavitro's line (envy, propel, activate, and synthesis), following the recommended dosing schedule
My Observations:
  • According to the pH/KH/CO2 chart, I should have a CO2 concentration of around 38 ppm (which I assume is a safe estimate, since I am remineralizing RODI water with only carbonate hardness)
  • However, my drop checker in the tank is very blue
  • Given Tom's earlier reservations about only relying on pH and KH values to determine CO2 concentrations, I am assuming the drop checker is correct and that I should change the control band on the APEX to drive my pH lower and increase CO2.
  • The Discus (and other tank inhabitants) should be OK as long as I keep pH above 6
My Concern:
  • I have read that it is important to limit the fluctuation of pH to no more than 0.2 in 24 hours
  • While I can slowly drop the pH to a new target (perhaps 6.2) over several days, I am concerned about how much the pH will fluctuate each time I perform a water change. The new re-mineralized water will still come in at a pH of around 7.8 (assuming I continue to adjust its Alkalinity)
  • At the same time, I've read other posts here from folks who seem to have routine fluctuations of pH greater than 1 over the diurnal cycle (due to timing CO2 injection with the light cycle)
  • I'm also worried about keeping the fish in water so close to a pH of 6

My questions:
  1. How much can pH swing in a relatively short period of time without distressing the fish?
  2. Depending on the above, when I perform a water change, should I introduce new water that has only been re-mineralized for GH (so there's not a swing in pH in the tank) and then slowly add buffer to the tank until I restore KH to my target?
  3. Outside of water changes, would it be better for the fish if I added more buffer to the water (Carbonate), instead of trying to keep the pH so low? (this stuff isn't cheap)
  4. Am I over-thinking all of this?
Thanks in advance for your guidance.
 

burr740

Micros Spiller
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Feb 16, 2015
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Now THAT's how you present a question! :)

1. PH swings from CO2 alone are not a problem for livestock. The end result is all that matters, how fast you get there doesnt.
2. Not sure I understand this one. Just reconstitute the water going in to match the water coming out and there should be little to no change?
3. A discus person would know this better than me
4. Yes I believe so, but it doesnt hurt to err on the side of caution
 

evangemeren

Junior Poster
Oct 5, 2013
19
2
3
Burr740,

Thanks for the insight.

With respect to my question (2): the concern here is that the re-mineralized water, before entering my tank, has a pH of >7.8 as a result of adjusting the KH to 4. Since the pH of the tank is controlled to 6.7, the introduction of the new water causes the pH to swing in the tank for a period of time ... by as much as 0.5 to 0.6 until the CO2 builds up and stabilizes the tank again. Given my understanding that a change in pH of more than 0.2 in 24 hours is bad for the livestock, I was concerned that my approach to water changes was hurting my fish.

To your point, I can't reconstitute the water going in to match the water going out since the later is saturated with CO2 (and therefore has a lower pH).

My alternative was to not buffer the new water as much so that it would have a lower pH (and thus prevent large swings inside the tank), but then add buffer to the tank right away to drive KH back to target.

Anyway - if it really doesn't matter how quickly the pH swings, then this really isn't a problem after all, and I can keep doing water changes the way I am.

Does anyone see this differently?
 

LRJ

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Aug 11, 2014
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A couple of things here. In order to get a more accurate assessment of your CO2, measure the relative drop in the pH of your tank water, instead of relying on the drop checker or the pH/KH/CO2 chart. Take a cup of tank water and let it de-gas for 24 hrs, then measure the pH. Compare that with the 6.7 you're maintaining in your tank. If you're getting at least a one point drop, you're probably good on CO2.

Here's the tricky thing though. Because you have a buffering substrate, your KH may be declining in between water changes. By holding pH at 6.7, your CO2 concentration is going to decline in between water changes as well if KH is declining. You do frequent water changes, so it may not be a huge issue in your case. It's something to be aware of though, because plants like stable CO2. This is one of the drawbacks of using a pH controller with a buffering substrate.

I have no experience with discus, but I have read that fish generally don't mind pH fluctuations in and of themselves. It's GH and KH fluctuations that are more important. So if I were you, I would prioritize stable KH, with regard to item (2) in your list. Match the KH of the tank, not the pH. Let the pH spike at water change and then bring it back down with the CO2. This is what I would do, unless told otherwise by an experienced discus keeper.

One final point, since you mention that the buffering product is expensive, have you considered simply cutting your tap water with RO in order to soften it to the desired level. Depending on how far apart your tap's GH and KH are, you might be able to get close enough to your 4GH and 4 KH targets just by using a tap-RO mix and forget the expensive products.
 
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Wobblebonk

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Jul 3, 2018
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I agree you should check the kh/degassed ph levels of the water coming out...

Google some diurnal ph water studies, I can't find data specifically on discus habitat but ph in rivers/lakes/ponds/streams with algae/plants can easily reach ph swings over 1 per day on bright summer days.

I personally think the whole concept of maintaining a ph through co2 levels 24 hours a day for livestock is mostly just wrong. I can't imagine this is what discus breeding operations are doing... but I could be completely wrong about this I don't truly know.
 

Greggz

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You have a lot going on there with that tank. My first thought is where are the pictures???

A couple of observations to add on to replies above.

I also use RO water. All you need is MgSO4, CaSO4, and K2CO3 to remineralize. It would be much cheaper in the long run, as it looks like those Aquavitro products come in liquid form, which in general is more expensive than dry.

And something about your KH/pH reading does not seem to make sense. You say KH is 4 and reading is 7.9??? At KH 4 I would expect pH to be around 7.4 or so fully degassed. Might explain why drop checker is still blue dropping to 6.7. Not sure what is going on there, but doesn't seem to add up properly.

Like others above, I don't think speed of pH change from CO2 injection is any issue. I drop mine in less than an hour about 1.35.

And given every question and answer provided, it probably all needs to be filtered through the lens of keeping Discus. They are a species that seem to be more sensitive than most. I would seek out some folks who are well experienced with Discus to get their thoughts as well.

Good luck and post some pictures!!
 
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Zeus

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Adding CO2 and dropping your pH is not changing the hardness nor alkalinity of your water

Think the alkalinity of the water does change because of the carbonic acid produced
upload_2018-7-8_14-42-1.png

____________________________________________


Well I Have been dropping the pH in less than 1hr daily in 500l tank for over a year with my duel CO2 injection without an issue, using about 6.5Kg of CO2 a month. Thats not just the DC lime green its the DC yellow to nearly clear. pH drop well over 1.0pH checked with Hanna pocket probe. I need more flow to keep plants/carpet healthy and until the product is released in September I am compensating the flow issue with very high [CO2] to keep the supply of carbon steady to the plants with the light levels I use. The DC to green which use to be adequate before the Biomass increase and reduced flow took about 30mins. Getting to the highest pH drop the livestock can handle really does use a lot of CO2.

How quick does a river change its pH when there is a sudden downpour of rain as for small streams it must be very quick
 

Phishless

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Carbonic acid is not strong enough to destroy carbonate hardness.
I've detected no difference in GH or KH between day and night in any tank regardless of CO2 (pH) levels.
 

Wobblebonk

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its my understanding that while youre pumping it in some carbonates form bicarbonates that precipitate back into carbonates when it degasses... but carbonates remain as opposed to like nitric acid or some such
 

Zeus

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Carbonic acid is not strong enough to destroy carbonate hardness.
I've detected no difference in GH or KH between day and night in any tank regardless of CO2 (pH) levels.

Think I know where your coming from, Gh and Kh remaining relatively the same regardless of CO2 injection, but the pH does change pre CO2 on to lights on if it didnt the pH meter wouldn't change

my understanding that while youre pumping it in some carbonates form bicarbonates that precipitate back into carbonates when it degasses...

Mine too
 

Wobblebonk

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the point remains, https://en.wikipedia.org/wiki/Alkalinity#Addition_of_CO2

Addition (or removal) of CO2 to a solution does not change its alkalinity, since the net reaction produces the same number of equivalents of positively contributing species (H+) as negative contributing species (HCO3− and/or CO32−). Adding CO2 to the solution lowers its pH, but does not affect alkalinity.
At all pH values:
CO2 + H2O ⇌ HCO3− + H+
Only at high (basic) pH values:
HCO3− + H+ ⇌ CO32− + 2H+

hardness and alkalinity are not basicity
 
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Zeus

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the point remains, https://en.wikipedia.org/wiki/Alkalinity#Addition_of_CO2

Addition (or removal) of CO2 to a solution does not change its alkalinity, since the net reaction produces the same number of equivalents of positively contributing species (H+) as negative contributing species (HCO3− and/or CO32−). Adding CO2 to the solution lowers its pH, but does not affect alkalinity.
At all pH values:
CO2 + H2O ⇌ HCO3− + H+
Only at high (basic) pH values:
HCO3− + H+ ⇌ CO32− + 2H+

hardness and alkalinity are not basicity

I stand corrected :eek::rolleyes: it has been some time since I did chemistry ;)

If you dont stick your neck out to what you think is correct you never learn
 

Wobblebonk

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i was confused myself, the previous thing was if you have limestone or something in a high ph tank. co2 then does what i said, temporarily increasing alkalinity and dissolving your limestone or coral or what have you slowly, but then precipitating that back out elsewhere in the tank later... never lowers your alkaliniy though
 

Allwissend

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I'm unclear on one key detail: how quickly can you drop the pH in the tank (to achieve the required CO2 concentration) while still keeping the inhabitants safe?

Background:
  • I've got a 130 gal. "high tech" planted tank (high lighting, CO2) with Ultum Nature Controsoil (buffers the water) and several large pieces of Malaysian driftwood.
  • I run it with a 40 gal. sump in the stand so I can keep all of the equipment hidden from sight.
  • The tap water in my area is basically liquid rock ... so instead I use RODI water that I remineralize to 4 dKH using Aquavitro Carbonate, and to 4 dGH using Aquavitro Mineralize and Seachem Discuss Trace
  • The new water has a pH of around 7.8 to 7.9 before being added to the tank
  • I have Discuss in the tank, along with a few bushynose Plecos, Rainbow fish, Siamese Algae Eaters, Greman Blue Rams, and Tetras
  • The tank is quite heavily planted with several slow-growing species of Anubias, Buce, and Amazon Swords
  • In case it is relevant, the tank stays at 82 degrees F.
My Observations:
  • According to the pH/KH/CO2 chart, I should have a CO2 concentration of around 38 ppm (which I assume is a safe estimate, since I am remineralizing RODI water with only carbonate hardness)
  • However, my drop checker in the tank is very blue
  • Given Tom's earlier reservations about only relying on pH and KH values to determine CO2 concentrations, I am assuming the drop checker is correct and that I should change the control band on the APEX to drive my pH lower and increase CO2.
  • The Discus (and other tank inhabitants) should be OK as long as I keep pH above 6
My Concern:
  • I have read that it is important to limit the fluctuation of pH to no more than 0.2 in 24 hours
  • While I can slowly drop the pH to a new target (perhaps 6.2) over several days, I am concerned about how much the pH will fluctuate each time I perform a water change. The new re-mineralized water will still come in at a pH of around 7.8 (assuming I continue to adjust its Alkalinity)
  • At the same time, I've read other posts here from folks who seem to have routine fluctuations of pH greater than 1 over the diurnal cycle (due to timing CO2 injection with the light cycle)
  • I'm also worried about keeping the fish in water so close to a pH of 6

My questions:
  1. How much can pH swing in a relatively short period of time without distressing the fish?
  2. Depending on the above, when I perform a water change, should I introduce new water that has only been re-mineralized for GH (so there's not a swing in pH in the tank) and then slowly add buffer to the tank until I restore KH to my target?
  3. Outside of water changes, would it be better for the fish if I added more buffer to the water (Carbonate), instead of trying to keep the pH so low? (this stuff isn't cheap)
  4. Am I over-thinking all of this?

To address just primary question, I don't know the answer but I strongly believe that it has to be a significant drop in a very short time, if one were able to alter the pH only by altering the balance of H+ and -OH. However in our aquariums a difference in pH can often caused by many factors ... so what caused the drop in pH is the more important question.

For this topic, the pH drop is caused by CO2. pH change from CO2 in 24 of 1-1.5pH are common. Usually most target this drop in 1-2 hours. pH changes from CO2 in nature all the time, especially in places with lots of algae or plants. Freshwater fish are a lot more flexible and capable to adapt different waters, as they do in nature. In my opinion the statement about the 0.2pH change is false (as shown by common practice) without further classifications on what caused that change and in what species. I read/hear people go on about the need for stability and stable pH but they never mention how GH, KH, TDS changes are much more important. GBR going from pH 6.7 to 5.5 daily breed and grow without problems.

When you perform a water change only introduce water at the same GH and KH as your aquarium (unless you want to change something).

Now, different fish have different resistance to CO2 levels. This not only varies between species, but also between individuals and what is more in the same individual. Fish are capable of adapting to higher levels of CO2 in the water if they are acclimated slowly. One individual may gasp at Xppm CO2 if suddenly increase while behaving normally at the same X if it was raised over several weeks.

The pH-KH-CO2 chart is not precise in aquariums, you have a lot of acids and bases interacting and being produced. It's not the pure experimental water used for the calculations. CO2 controller and buffering substrate is a little defeating the purpose depending of the reactivity of the soil. LRJ already provided good advice on the topic. With the plants you have and as the fish are 1st priority I see no need to go very high with CO2.


Adding CO2 and dropping your pH is not changing the hardness nor alkalinity of your water.
Typically the full pH drop is done over 1-1.5 hours before lights on.
This is correct. There is an exception worth mentioning. If you have a solid source of (CO3)2- in the tank or filter like stones containing limestone, crushed coral etc... In this case the acidic pH (caused by the CO2 injection) will dissolve extra carbonates in solution which will stay there even after CO2 degassed, this results in increased KH and most often also increased GH. I don't think this is the case of the OP but worth mentioning in case someone reads it.

Lastly, go slow and watch the fish. They are first. Give them time to adapt and watch for any signs of stress.