Ph Swings, waterchanges etc!

[BrendanJ23]

Well more co2 is present when lights are off because plants are not consuming it, but also releasing it, as are the fish.
Then as it is consumed during the day, the PH rises. I have confirmed tonight that there is much less swing in PH with majority of plants removed from the tank. I will monitor this over the next few days for consistency.

[dspeers]

Brendan, with CO2 users, there seems to be some debate regarding whether pH swings associated with fluctuating levels of CO2 are as harmful as lowered pH from other sources. I don't know why the nature of the conjugate base would have any impact on the effects of fluctuating pH. When I get my tanks set up I want a lot of plants but do not intend to test the effects of daily pH fluctuations. Regardless, pushing your kH up will lower the degree of pH fluctuation but the "fix" is to either reduce the number of plants, add CO2 during the day, or increase offgassing by increasing surface area either with more airstones, &/or adding a sump, &/or adding wet/dry filtration, &/or fluidized filter &/or spray bar for water return. My tank design includes all of these, I like redundancy.

[bluelagoon]

Plants will not flourish in that PH. Generally a PH of 5.5 - 6.5 but can go a bit higher. Usually not higher than 7.5 and some plants even have a difficult time taking up nutrients in that PH.

[dspeers]

Plants will not flourish in that PH. Generally a PH of 5.5 - 6.5 but can go a bit higher. Usually not higher than 7.5 and some plants even have a difficult time taking up nutrients in that PH.

No argument in re aquarium plants in general but at the same time the 0.5 ph swing indicates that whatever type of plants he has, they are metabolically active suggesting good health. Brendan, purely for my curiosity, once you pulled the plants, did your ph trend closer to 8 or 7.5?

[BrendanJ23]

No argument in re aquarium plants in general but at the same time the 0.5 ph swing indicates that whatever type of plants he has, they are metabolically active suggesting good health. Brendan, purely for my curiosity, once you pulled the plants, did your ph trend closer to 8 or 7.5?

Hi Don,

The tank only drops to about 7.9-8.0 at night, and peaks at about 8-8.1 during the day.

[BrendanJ23]

Plants will not flourish in that PH. Generally a PH of 5.5 - 6.5 but can go a bit higher. Usually not higher than 7.5 and some plants even have a difficult time taking up nutrients in that PH.

What’s the theory behind that Merv? I ask because I’ve always had plants grow and flourish in that PH range, I’m currently trimming about 3ft of growth off my vallisneria each month and I recently had my swords produce about 40 pups.

[dspeers]

So basically your ph swing was due to an accumulation of CO2 when dark rather than exuberant photosynthesis raising your ph during the day. If you are satisfied with plant growth then the first problem can be addressed by increasing the effective water surface area. Had it been the second issue, would have either required adding CO2 during the day or keeping the plant biomass way down as you have already done. My understanding of the negative effects of alkaline water on plant growth is that several important nutrients, Iron, Calcium, etc. become less soluble as ph goes up causing deficiencies.

[BrendanJ23]

So basically your ph swing was due to an accumulation of CO2 when dark rather than exuberant photosynthesis raising your ph during the day. If you are satisfied with plant growth then the first problem can be addressed by increasing the effective water surface area. Had it been the second issue, would have either required adding CO2 during the day or keeping the plant biomass way down as you have already done. My understanding of the negative effects of alkaline water on plant growth is that several important nutrients, Iron, Calcium, etc. become less soluble as ph goes up causing deficiencies.

Ok, so increasing the effective surface water area means either a wider tank or sump? How does this affect it?

My end goal is to be able to have plants, with minimal PH swing.

[Sturiosoma]

Plants will not flourish in that PH. Generally a PH of 5.5 - 6.5 but can go a bit higher. Usually not higher than 7.5 and some plants even have a difficult time taking up nutrients in that PH.

I kind of disagree with you here Merv as all of my tanks are planted my lowest ph being 6.8 and the highest being 7.2 I target feed on the initial startup of a tank but nothing afterwards I do not run co2 I run my lights 12hr a day and my plants are flourishing I think it comes down to fine tuning a tank, generally you can do a 30% water change with no adverse effects on ph

Jeanne

[bluelagoon]

I kind of disagree with you here Merv as all of my tanks are planted my lowest ph being 6.8 and the highest being 7.2 I target feed on the initial startup of a tank but nothing afterwards I do not run co2 I run my lights 12hr a day and my plants are flourishing I think it comes down to fine tuning a tank, generally you can do a 30% water change with no adverse effects on ph

Jeanne

Plants will grow in that range. Not too high. My water is soft, is similar to yours. They would do much better between 5.5-6.5. but a few degrees on side or the other and most plants will do ok (5.0-7.5). But 8, I don't think you'll find many fresh water plants that can handle that much alkalinity. I see nutrient imbalance.

[bluelagoon]

oops double post

[dspeers]

Off-gassing the excess CO2 produced by the plants overnight first requires sufficient water circulation in the tank to avoid a concentration gradient, but with any reasonable flow (which you have with two canister returns) that should not happen. Your rate limiting step for removing CO2 is the total surface area between water and air. All aeration does is increase this interface by the size and number of the bubbles, same goes with either a fluidized biofilter https://www.youtube.com/watch?v=U9ovPRxMWk8 or a wet/dry chamber https://lovefishtank.com/wet-dry-sump-filter/ Since I am using both, I have a filter pad in the base of the box and use K-1 media in the fluidized filter. Adding a spraybar to the canister or sump filter return increases surface area, drilling a bunch of holes in the top of sump chamber separators to break up flow increases area. The fastest and easiest steps for you are to increase aeration with increased stones or bubble curtains, only need to run when lights off so aesthetics not an issue and add spraybars to your cannister returns. Reintroduce all the plants and see where you are at. If that still fails then would consider adding a sump. If you like your tank, that would be the last thing I change.

[BrendanJ23]

Hi Don,

Thanks for your help, sorry I thought I had already replied to you. I've added some aeration, more crushed coral and just two pots of val to the tank. I'll monitor this and see what happens.

[bluelagoon]

What is your rational for adding crushed coral for an already high KH and PH? Never heard of doing it on those water parameters for discus.

[dspeers]

That may be my fault. I indicated that increasing the Kh would reduce the ph swings at night. In addition he indicated that his Kh was 5-6 which is a little low in what I understand is proper Discus range 4-8.

There are still things about this tank that confuse me or I did not ask but should have. Given that he was able to stabilize the pH I kinda backed off, I can be a little OCD and did not want to be a PITA The biggest puzzle is that to my understanding unless tank circulation is very low or top is tightly sealed or tank design has very small air/water interface or Kh is under ~3.5, pH should not move by ~0.5 without supplemental CO2. Unfortunately none of these situations apply and I am concerned that I am still be missing something.

1. Why does his mechanical/Carbon filter drop the tap water pH from 8 to 7.5, not particularly important, but weird.
2. The pH in the aging barrel at 48 hours is 8.5, is that also heated or still substantially colder than the aquarium temp. If colder still supersaturated with CO2. Not that important in this case but the colder the water the higher the risk of "microbubbles"
3. Did you verify your Kh test results, and more importantly when did you test relative to your water change? If just post water change you do not know if that represents a swing of as low as zero or you added new water with a Kh of 10 to tank water with a Kh of 2. Would be advantageous to test the kH of the aging barrel and tank both just prior to a water change.

The implications of a wide swing is that your Kh is being consumed by another source of acid, probably NO3. So what is your nitrate level? Given that your pH varied more with day vs night than with water change I would be surprised if your NO3 is high but as mentioned your tank is confusing. If your Kh difference between barrel and tank is low this should also be low, but better to verify. Again testing both the barrel and tank just prior to a water change would be most informative.

If your Kh variance is low and is indeed 5-6, I agree with Mervin, raising it offers no substantial benefit, but in fairness changing the Kh from 5 or 6 to only 8 should not increase pH by all that much. If your Kh has major swings you have a different problem with a different solution and the plants are a diversion. But, the fact that removing plants fixed the problem should mean this is CO2 and only CO2.