[Danre]

Noticed something quite annoying when testing pH on my 10g planted tank, and don't know the cause. Here's the rundown:

Aquarium pH reads at ~8.2 with a GH of ~8 deg. Tap water pH reads at ~7.8 with a GH of ~13 deg.
I tested tap water that has been sitting out for 24 hours + as well as straight from the faucet, and got the same results in terms of parameters in hardness and pH, and has been the same predictable results for a number of years, as I live where there is hard water.

Tank has no rocks whatsoever, only spiderwood, plants, and BDBS. The water I put into the aquarium has .5 a gallon of DI water for ever 1.5 gallons of tap water, a 1/4 ratio, and I stay consistent with the ratio every water change. When I top off evaporation, I top off with pure DI water as well. Tank has no stock, only heavily planted, and currently cycling at 4 weeks old, ammonia and nitrite levels starting to lower, nitrates around 20ppm.

What's odd is my GH hardness has remained stable through the pH change but my KH values I have not tested yet, but I don't exactly know how they'd relate.

Are the plants lowering the pH of the water somehow? Any clues or input would be helpful.

Would also like to ask if this is related to gas exchange and plants utilizing Co2 in the water column to a point where the pH is raised. If this is the case, how could I mitigate this>

 

[Zoidburg]

KH can have a bigger impact on pH than GH... since you can have a high pH level with low GH or a low pH level with a high GH. KH plays a role... as does CO2, tannins, etc.

It's hard to say what to do since you are cycling a tank... and that can also skew the parameters.



So my best suggestion is to leave it be! You may have a better idea once the tank is fully cycled. Parameters may change! Or they might not... Just wait it out either way.


Do you need lower pH for any reason?

 

[Mark Fisher]

If you check your tank pH before the lights come on (i.e., before your plants start utilizing CO2), you should be able to see if photosynthesis is raising your pH.

 

[Danre]

KH can have a bigger impact on pH than GH... since you can have a high pH level with low GH or a low pH level with a high GH. KH plays a role... as does CO2, tannins, etc.

It's hard to say what to do since you are cycling a tank... and that can also skew the parameters.



So my best suggestion is to leave it be! You may have a better idea once the tank is fully cycled. Parameters may change! Or they might not... Just wait it out either way.


Do you need lower pH for any reason?

I should double check my KH then for sure, and also test during different parts of the day to see if plants are really doing it.

For the reason of my worrying, I'm just bit concerned that water changes of any percentage in a tank this small with create drastic pH swings, especially when I have livestock later on. But other than that, its just something that I noticed with no real answer I could come up with, but I really will just have to wait until it's finished cycling.
As for me cutting my water with distilled, it's only to reduce the hardness just to a more reasonable range without overly tampering, I think I'm contempt with my high pH, but this threw a curveball in my perception.

 

[Zoidburg]

Most people do not have an issue when there's a change in pH levels....

And the only time they typically do is generally when they have a tank set up incorrectly... i.e. a tank with active substrate that lowers the pH and the person is using tap water instead of RO or distilled with GH minerals.

In your situation, I don't think it would be that big of an issue... perhaps what you are worried about is "pH shock", which is in fact not a thing...it's actually "TDS shock", or the correct term, osmotic shock. It would be like taking a fish that's in a tank with 6 GH and shoving them into a tank with 15 GH or visa versa. It's a change in pressure and different levels can effect their length of life... Many tetras for example are a soft water species. Sure, they can live in hard water! However, they are prone to kidney failure in harder water. The effects may not be seen immediately, but over time.

This is made more difficult when people don't have a true understanding of what hard or soft water is.... I see many people assume that high pH means hard water, lower pH means soft water... which isn't necessarily true... since a lot of things can alter pH. Add in the fact that you can't always find reliable information on where the fish come from in the wild so you don't know the exact parameters in which they thrive in best...