Top Fin gravel questions

[ArtistGardener]

Anyone have problems with using Top Fin brand black gravel? The PH in my tanks is going up slowly even though I do a 20% water change every week and my tap water remains the same. I am going to run some tests (test my conditioned tap water in a cup, then add a layer of gravel and test again in a few days), but I am wondering if anyone has had problems with this particular brand.

 

[my_little_tetra]

I have Top Fin brand gravel in my 29g and 3g, but it is "natural" color. The pH in my tanks is the same as the pH of my tap water.

 

[Riot84]

I have the top fin black gravel in my Oscar tank and the ph is the same as the tap.