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Low hardness but high pH?

Blanchedalmond

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Hey everyone, I've got a query that I'm struggling to solve about water chemistry.
There are no fish in this tank, so it's not an urgent fix just looking to understand.

It's a 180L (roughly 47 Gallon), 120cm/4ft long tank. Has been setup for 6 months as a daphnia/micro invert/plant tank but was mostly drained and plants moved around 3 weeks ago. Substrate has remained the same, Oliver Knott Aqua Earth (different to what I used for my other tank)

After refilling with conditioned water, the pH moved from 7.1 up to 7.6 making me think there was something increasing the hardness of the water.

Upon testing General and Carbonate hardness it was identical to fresh out of the tap, 3 degrees general and 2 degrees carbonate.

I definitely expect a pH swing on such soft water, but after testing every day for 3 weeks the lowest it has dropped is around 7.4 and didn't stay there long.

All tests have been the API liquid drop test kits, the tank is planted and has moderate amount of driftwood, only rock is granite (no reaction to acids while testing before scaping), running a basic dual bubble filter setup and LED light.

Process of elimination is making me lean towards adding a GH buffer in small amount if it's an instability issue but the aqua soil mentions it "lowers GH" so I don't want to mess with something I don't yet understand fully.

If you made it through this essay length explanation, thankyou for your patience and if you have any ideas or advice I'm eager to hear any possibility😊
 
Tap water is under pressure and this can drive out dissolved gasses like nitrogen (N), oxygen (O2) and carbon dioxide (CO2). If there is more CO2 in the water when it comes out of the tap, the pH will be lower than the same water that has been aerated or allowed to stand for 24 hours.

The other reason the pH can go up is due to plants. Live plants will use up CO2 when they get light and this can cause the pH to increase due to more oxygen in the water.

Take a sample of tap water and test the pH. Leave the container of water on a shelf for 24 hours and test the pH again. The pH of the water 24 hours after it was taken from the tap is the more accurate pH of your water.
 
Tap water is under pressure and this can drive out dissolved gasses like nitrogen (N), oxygen (O2) and carbon dioxide (CO2). If there is more CO2 in the water when it comes out of the tap, the pH will be lower than the same water that has been aerated or allowed to stand for 24 hours.

The other reason the pH can go up is due to plants. Live plants will use up CO2 when they get light and this can cause the pH to increase due to more oxygen in the water.

Take a sample of tap water and test the pH. Leave the container of water on a shelf for 24 hours and test the pH again. The pH of the water 24 hours after it was taken from the tap is the more accurate pH of your water.
The testing water that's too fresh sounded like the culprit, but I age our tapwater 48hrs for my 3ft tanks water changes (the fish seemed to dislike the unaged water, probably due to what your first point mentions) and it tested 7.2, which that tank also tests stable at.

The plants sound like the most likely candidate, would longer than necessary light hours be making it more pronounced?

Thankyou so much for all the info behind why each of those things could be the answer, you'd be a great science teacher😁
 
The more plants in an aquarium, the more CO2 they use.
If the lights are on for a long time, the plants can photosynthesise for longer and use more CO2 with the same result, a lower CO2 level and higher O@ level that can raise the pH during the day. At night the pH can drop if there are lots of plants because they use the O2 and release CO2. This issue with plants causing the pH to fluctuate during the day and night can be limited or prevented by having lots of aeration/ surface turbulence.

If you have chlorine in the tap water (most Australian cities do), the chlorine will come out after a few days of water standing in buckets. This would make it safer for the fish compared to using water straight out of the tap. If you use a dechlorinator, it will neutralise chlorine when it comes into contact with the chlorine molecules. This can happen quickly (within a few minutes) if the water is aerated because the aeration can help the dechlorinator and chlorine molecules come in contact faster.
 
If you are going to test the theory, only do one thing at a time.
eg: reduce lighting by a couple of hours a day for a week and monitor the pH.
The following week have the normal lighting schedule (not reduced lighting) and increase aeration for a week. Monitor the pH.

If you do both at the same time, you won't know which one (if either) are causing the issue.
 
What fish are you planning to keep? There is no ideal value but different fish do better in different water. Most soft water fish will be fine in a pH of 7.6. Each tank is different - I have 3 tanks that use identical water and similar plants, wood etc. and all have a different pH. I don't stress about it and neither do my fish. Since my KH is zero I do tend to change 75% of the water every week and this keeps the pH stable.
 
I have a friend who has a well that gives him high pH, low mineral content water. It's stable. I've seen wild caught Discus breed and tend babies in his tanks, 2 weeks after they arrived. Unexpected? No kidding.

It's a reason I suspect pH is not as important as some make it out to be, but hardness is crucial.
 
I have a friend who has a well that gives him high pH, low mineral content water. It's stable. I've seen wild caught Discus breed and tend babies in his tanks, 2 weeks after they arrived. Unexpected? No kidding.

It's a reason I suspect pH is not as important as some make it out to be, but hardness is crucial.
This isn’t the first story like this I’ve heard . I am inclined to agree that pH may not be as important as guys think . Anyway , water chemistry is baffling . It is almost impossible to change pH but hardness is easily overcome with a reverse osmosis unit . The pH seems to always revert to its original reading unless you can prepare water in a large container with something to buffer it one way or the other . Easier to go alkaline than to the acid side .
 
Low pH usually means low hardness, as a rule of thumb. But I worked in enough places where rule of sawblade was way stronger than rule of thumb when it comes to measuring things.
Water is a mysterious thing.
I bred Apistogramma njisseni, wild caught at zero hardness and a pH of 5.5 in absolute blackwater. I could get excellent numbers at pH 6.6 or 6.8, to the point I felt they were easy to breed. But I needed to use reverse osmosis, rainwater or snow melt to get to the very low hardness they needed for anything to happen. The pH looked high for the species, but breeding success was with the minerals.

pH is easy to read, so I think in many cases, it became THE measure.
 
If you are going to test the theory, only do one thing at a time.
eg: reduce lighting by a couple of hours a day for a week and monitor the pH.
The following week have the normal lighting schedule (not reduced lighting) and increase aeration for a week. Monitor the pH.

If you do both at the same time, you won't know which one (if either) are causing the issue.
Too easy, lights this week then revert the changed light hours and try surface agitation for a week?
I'll try to remember to treat it like science, only one stimulus change per "experiment" or the results mean nothing😅
 
What fish are you planning to keep? There is no ideal value but different fish do better in different water. Most soft water fish will be fine in a pH of 7.6. Each tank is different - I have 3 tanks that use identical water and similar plants, wood etc. and all have a different pH. I don't stress about it and neither do my fish. Since my KH is zero I do tend to change 75% of the water every week and this keeps the pH stable.
Definitely more a standard community setup (likely bronze corydora and phantom tetra or very similiar) than any super acidic lovers so it sounds like you're on the money.
Even just knowing the tanks can sit at different pH from the same source is a huge relief🫡
 
I have a friend who has a well that gives him high pH, low mineral content water. It's stable. I've seen wild caught Discus breed and tend babies in his tanks, 2 weeks after they arrived. Unexpected? No kidding.

It's a reason I suspect pH is not as important as some make it out to be, but hardness is crucial.
I guess maybe it's easier for them to regulate their body pH to the water pH than to osmoregulate minerals in or out of their body? Sounds like I have a lot of reading to do😁
 

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