Rock Id Help?

I put some rocks that the previous owner(he kept cichlids) gave me into my aquarium to make some hiding spots before I get some plants...I suspect they are raising my pH. This morning's reading was somewhere around 8.3 and I'm concerned for my new corys (glass surfing). Can anyone help ID - do I need to take them out?

 

Basalt rock. And the flat one looks like slate.

 

Looks like limestone. If it is powdery when dry, and etched, most likely is raising pH.

 

The purple one & the flat green one on top of it on the right look like slate to me, I have some of the same as the purple one, the others on the left I don’t know.

Edit: forgive my manners I forgot to say Welcome to Fishlore

 

Basalt rock. And the flat one looks like slate.

Yeah the flat one is almost assuredly slate. If Basalt we should be good for aquarium.

Looks like limestone. If it is powdery when dry, and etched, most likely is raising pH.

Which one, the ones one the far left with quartz in them?

I forgot to mention I think the brown one is some kind of manufactured rock for aquariums so not too worried about it.

I did just add a small amount of dry sphagnum moss to my filters, in two out of four cartridges, we will see if that can help keep me closer to the high 7s.

 

Yeah the flat one is almost assuredly slate. If Basalt we should be good for aquarium.



Which one, the ones one the far left with quartz in them?

I forgot to mention I think the brown one is some kind of manufactured rock for aquariums so not too worried about it.

I did just add a small amount of dry sphagnum moss to my filters, in two out of four cartridges, we will see if that can help keep me closer to the high 7s.

Agree if it's basalt, it should be inert. Sorry I thought the quartz was etching. I had some limestone rocks that looked like that. They were powdery to the touch when dry, that was my alert that it would dissolve and raise pH. And they did.

 

It is normal for corys to glass surf when they are new to the tank. I don't think the PH level has anything to do with it. Just give them time to settle in. Most corys will settle down after they get used to their new home.