pH problem

[Byron]

You could change from Fluval Grow to Flourish Comprehensive Supplement or Brightwell Aquatics' FlorinMulti. I've been using the Flourish Comp for over ten years with excellent results (along with the tabs for larger swords, even these on their own).

Before considering more complicated options, now that you have mentioned the white substrate material that may well be the source of the calcium raising the pH. The test @seangee suggested should determine this one way of the other, and if it is as I suspect, replacing the substrate with inert sand will be your option. You will never get acidic water if there is calcareous material in the substrate. Using such a substrate was how I kept my pH and GH high for livebearers years ago, and it worked very well.

 

[Animallover😍]

Ok, I'll change to flourish. Thanks for the suggestion! Testing my substrates, one container just tap water, one with big white rocks, one with small white rocks, and one with small black rocks.

 

[Animallover😍]

I tested my substrates.
Tap water: 6.8
Big white stones: 7.2
Small Black stones: 7.6
Small white stones: .2

CO2 outgassing could drive the PH change. tap water in many places is sterilized by adding a small amount of Chlorine gas. Some of this chlorine will then react with Carbonate salts (KH) such as CaCO3 (Calcium carbonate). That reaction converts CaCO3 to CaCL2 (calcium chloride) and HCO3 (carbonic acid) and then the water is put in the pipes. While it is in the pipes everything stay stable and the excess HCO3 makes the water slightly acidic. However when the water is put into your tank HCO3 converts to CO2 and And the excess CO2 is lost to the air. As CO2 outgases the PH will then go up as the CO2 concentration drops. The PH then stabilizes to a value consistent with whatever minerals are dissolved in your water.

I think this is the reason that the tap water alone is 6.8, and the cause of the pH rising are the black small stones, which are scattered all over the aquarium and have the same jagged look like limestone. But just to make sure, I'll test again today.
This is the gravel I bought

Aquarium Sand 1KG (White / Black / Yellow) | Lazada

pepek palsu untuk lelaki sand. pasir putih halus aquarium. aquarium sand for plant. driftwood for aquarium. aquarium wallpaper 3d

www.lazada.com.my

 

[Animallover😍]

If it is the cause, I'm getting sand.

 

[seangee]

Just to make sure do the same test with a handful of the sand. The link does not give any details about the sand - so best to rule that out as another potential factor.

 

[Byron]

If it is the cause, I'm getting sand.

Seangee's post caused me to check the link again, --that is what you have now, isn't it? And the white is likely calcareous.

 

[Animallover😍]

yes, it's what I have now, not what I am getting @Byron

The link does not give any details about the sand - so best to rule that out as another potential factor.

The link was the current substrate