# diurnal pH fluctuation and fish health



## peridot (Feb 24, 2005)

Hi All
The pH in my tank routinely varies between 6.8 and 7.6 or 7.7 depending on when I test it. It is low just before the lights come on and high at the end of the "day". Pretty wide swing, I'd say. Has anybody else noticed this? Think it maybe fairly hard on the fish but I cannot figure a way to prevent it. Maybe it does not matter.....

I have successfully kept Walstad soil based tanks for 12 or more years and this behavior not uncommon. My current tank is two years old, soil based, and I keep the water hardness around 6-8. I do a water change 2-3-4 times a year. Lighting is compact fluorescent with a two hour siesta. The schedule has low light periods of 1.2 watts/gallon lasting 4 hours total (dawn and dusk). The central part of the day consists of 8 hours of 2.4 watts/gal. The plants are doing just fine; I cut them back routinely or there would be no room for the fish. Fish health is reasonable but maybe not great. The fish are mostly tetras, neons, and corydoras. Their appetite seems not robust, which concerns me some. Did water tests nitrite, nitrate ammonia, and water change, added carbon within the last month. No change in behavior; also no deaths nor obvious illness .

In an earlier lifetime I operated a wastewater treatment facility whose final treatmment step was a "polishing lagoon" , basically a big pond, complete with ducks and frogs. The pH in that thing would swing wildly in the May, June and July when the algae would would bloom. Maybe i have too much light?

thank you for your patience and your perspectives

Mary


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## peridot (Feb 24, 2005)

Forgot to add that I have to keep oyster shells in the filter bag or the pH will go down to the mid 7's (or lower) within hours. Yikes! And the tank is a 30 gal


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## peridot (Feb 24, 2005)

*swinging pH*

I think maybe I put my question a little to formally (below:diurnal pH fluctuation and fish health)

Has nobody noticed a change in their pH depending on how many hours their lights have been on?


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## HDBenson (Sep 24, 2014)

Hi peridot! What you are experienceing is a natural occurrence in NPTs. There are a few thing happening in your tank. What is happening is acidification - CO2 and natural acidification from breakdown of organic compounds. First the CO2 aspect: during your siesta periods CO2 is biulding up in your tank(this is why Walstad doesn't talk about injecting CO2 in her method). In short, when lights are off aquatic plants switch from producing oxygen to CO2. During both siesta and light on times certain bacteria are also producing CO2 from the breakdown of organics. Also, through respiration your livestock is creating CO2. During the siesta CO2 levels are steadily rising because plants/algae aren't uptaking CO2. CO2 deacreases pH - a common occurrence in CO2 injected systems. At the same time the natural decomposition of organic compounds is constantly going adding to the build-up of humic acids - this happens in all aquariums. To combat this you can increase your alkalinity(KH). KH is the ability to buffer water or, to maintain a stable pH. Check this parameter in both your tank and tapwater the next time you check your water. Something in the 800 ppm range shoulf be sufficient. There are many affective ways to raise this value. A quick Google on pH buffering can give you several easy ways to do this. One of the more common ways is adding Baking soda(not baking powder) to your water. But make sure you do this consistently and in small amounts. This will also increase your pH in tandem with your alkalinity. Yes, pH swings can be detrimental to fish health and, in some cases can cause drastic stress and even death if the swing is fast enough. If you have Ms. Walstad's book give it another read, she addresses this phenomenon throughout it. If not, then pick up a copy. Anyone doing Walstad tanks should have a copy even if it is just a reminder from time to time of small but important and easily forgotten bits of information that can help you out! Hope this helps!


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## Michael (Jul 20, 2010)

Peridot, I have combined your threads since they deal with the same issue. I agree with HD's reply.


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## peridot (Feb 24, 2005)

Thanks for your help. In error, I thought that was what the oyster shells were doing.... Ugh

Mary


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## HDBenson (Sep 24, 2014)

Certainly! That is what we are all here at some point or another. Let us know what your readings are when you get them and maybe we can help you more from there. Again, if you don't have a copy of _Ecology of the Planted Aquarium_ make sure you get a copy at some point. From what I understand there have been changes to her method in the last few editions. You can pick up the newest edition off Amazon for about $30.


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## peridot (Feb 24, 2005)

Oh, I have the book alright, have for years. Read and studied many times and as thoroughly as I can.
The crushed oyster shells I have been in all along. I generally avoid baking soda as it is too easy to get pH bouncing around but will use it if I have to. Using baking soda the goal is to raise the lower end of the swing, correct? That way the daily swing might be 7.3 to 7.7? Is that what you consider success, especially in a community tank with Corys and Tetras among others

Other than reducing the lighting, I cannot think of anyway to reduce the high end of the swing, can you?


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## peridot (Feb 24, 2005)

Forgot to add that alkalinity is 2 grains dKh, which is lowish


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## HDBenson (Sep 24, 2014)

Mmmm... when used regularly and in small quantities baking soda shouldn't do this. This should slightly raise your pH and increase your Kh. From what I understand GPG(grains per gallon) measures water hardness. While Kh and GH do go hand-in-hand they do not measure the exact same thing. Generally, GH can moderatly reflect what your alkalinity is. 2gpg is almost equivalent to 2dGh. This is very low hardness even with the oyster shells. I personally do not know if you can use gpg to measure alkalinity, I wouldn't think so. But if it is and you have an alkalinity that low then you are looking for something in the ballpark of 205 gpg dKh. But I am not too familiar with gpg regarding Kh and GH.


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## peridot (Feb 24, 2005)

I should clarify. I keep hardness (GH) between 6-8 by adding calcium chloride as is sinks over time. My mistake has been to not monitor kH (carbonate hardness) ? According to my API kit it is 2 dKh which converts to 35 ppm. On p 93 of the 2nd edition Diane recommends above 3 or 4 when using CO2. Am I wrong in thinking that 3 or 4 would be adequate with no CO2?

Part of the reason I wasn’t monitoring carbonate hardness was I was relying too heavily on crushed oyster shells. I think I have been skittish about baking soda as I used to use it without oyster shells and when it was exhausted the pH crash was swift and dramatic. Other bad memoriess from other contexts to complex to relate. Maybe the best is combining the two as the oyster shells would put a floor under things if baking soda doses get away from me. Or at least more oyster shells, and more finely ground ones….

My tap water has plenty of both GH (11) and kH is eight. I cut it 1/3 with rain water for water changes.

The siesta period has been only 2.0 hours; will expand it to a full 4 hours; that may help tame the pH peaks.

I am so grateful for your help; I am realizing that a stable pH is the goal regardless of what the ultimate pH settles out to be. Rereading Diane’s book last night I noticed an interesting comment on p 184: “All my tanks have an alkaline pH or 7-8, less than perfect for the plants, but I have learned to accept it” Maybe less than perfect for some community fish too, who knows? 

If I can moderate the peak pH and bring the alkalinity up so that the minimum pH approximates it, all is well, right? I might end up with a tank which swings from maybe 7.3 to 7.6 or something like that


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## HDBenson (Sep 24, 2014)

Very true that stable pH is much more important than a specific pH. Also, regarding your siesta schedule, increasing the amount of time the lights are out will increase your CO2 thus adding to acidification. With the exception of some wild collected species and very delicate species of both plants and fish many species from soft acidic water can and do adapt rather well to harder and more alkaline conditions. Conversely both plants and fish from harder more alkaline waters have a harder time adapting to softer acid conditions. Walstad talks about some softwater plants thriving in harder more alkaline waters due to the availability of more nutrients than the low nutrient softwater habitats they are used to. Do remember though - just like with fertilization, frequent small doses will do more help than one large dose. However, as long as you add the same amount with every water change you should be fine and quickly see your pH stabalize.


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