Tank pH compared to Tap Water pH

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PygmyMitch

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So i’ve done a pH test on my tank water and on my tap water, and they are different. What causes the pH levels in my tank to be higher compared to the water out of my tap ?
 

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Byron

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There is sometimes due to some calcareous substance in the tank. This could be the substrate, rocks, or sometimes certain decor. Are there rocks? And what material is the substrate?

Another factor can be the level of dissolved CO2 in the tap water. This will result in a lower pH reading, but when the CO2 dissipates out in 24 hours the pH will rise back up to its natural level. To determine this, let a glass of tap water sit 24 hours, then test the pH.
 
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PygmyMitch

PygmyMitch

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I have sand as my substrate, I have 1 rock and 1 ornament.

I will give that a go then, and see what the difference is to testing it straight out of the tap. Thanks
 

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Both the sand and the rock could be calcareous. If testing water which has stood for 24 hours doesn't account for the difference in pH, set up 2 containers, one with just water and one with some sand and water. Test after a week. If both are the same pH, it's not the sand, so repeat with the rock. But it's more likely to be something dissolved in the water gassing out.
 
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PygmyMitch

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Thanks for the suggestion Essjay. I can confirm that the water that has stood for 24hrs is still the same reading as yesterday at 6.8/7.0

So I have set up 3 seperate containers, one with just water, one with sand & water and the third with the rock & water. I have tested all of them to start off with, to make sure they are all the same and they are all reading a pH of 6.8 and pH high of 7.4

I will test them all again next weekend. and hopefully we should have answer! 🤞🏻
 
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PygmyMitch

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what color is your rock and do you have any seashells in the tank, dried corals?
The rock is a grey colour all over. some parts slightly lighter in colour than the rest. No seashells or dried corals
 
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PygmyMitch

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Well hopefully i will have the official answer next weekend when I test the waters again. Thanks for the input, I wasn’t aware that different rocks caused your pH levels to change
 
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PygmyMitch

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I think i’m starting to understand it better now, but correct me if i’m wrong. So looking up ‘calcareous’ it says this ‘Calcareous (/kælˈkɛəriəs/) is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky.’

and I do remember my rock being sort of chalky at one point when i had it out my tank a while back and it had dried. So obviously my rock must ‘leak’ (if thats the correct term) alkalinity which is why my tank water will have gone from being more acidic to being more alkaline ?

but i don’t understand what you mean by ‘it works faster on the rocks’ I’m assuming you mean there is a reaction between the water and rock that occurs faster because the water is more acidic and the rock is more alkalinity, which is what causes the rock to ‘leak’ alkalinity ?
 

Byron

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I think i’m starting to understand it better now, but correct me if i’m wrong. So looking up ‘calcareous’ it says this ‘Calcareous (/kælˈkɛəriəs/) is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky.’

and I do remember my rock being sort of chalky at one point when i had it out my tank a while back and it had dried. So obviously my rock must ‘leak’ (if thats the correct term) alkalinity which is why my tank water will have gone from being more acidic to being more alkaline ?

but i don’t understand what you mean by ‘it works faster on the rocks’ I’m assuming you mean there is a reaction between the water and rock that occurs faster because the water is more acidic and the rock is more alkalinity, which is what causes the rock to ‘leak’ alkalinity ?

The rock is not leaking something, it is slowly dissolving the minerals, primarily calcium. The lower the pH the more acid the water is, and this will work faster to dissolve or corrode or whatever. Rock that is limestone, marble, dolomite, aragonite is all calcareous, as are shells and coral. Snails and shrimp need calcium to build their exoskeletons, which is why they generally do better in harder water with a basic pH, though there are exceptions. This is very general.

Let the three buckets sit for the week. We don't want to make assumptions, and it will be helpful to know just which substances are contributing.
 
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PygmyMitch

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Yeah thats makes sense, I understand what you’re saying. Obviously im probably never going to be able to see it, but i’m guessing the rock would very slowly, over a very long period of time, shrink in size, due to the minerals in the rock dissolving.

Yeah 100% i was going to leave the buckets as they are anyway. I am interested to see if the sand is also playing a part in the tank pH levels. It will be interesting to see the pH level change / or not change in each bucket. definitely learned something new today. thanks!
 
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PygmyMitch

PygmyMitch

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Just a quick update on the three buckets. 4 days in, and the bucket of water with the rock now has a slightly higher pH than the other two buckets. (see attached photo)

Seems as though, the rock is the cause for my pH levels in my tank being higher than my tap water. I’m going to leave the buckets till sunday night, and do another test to see if it increase much more
 

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