Lava Rock - another question.....

[ianmianmianm]

Happy new Year all.

Unrelated to my prior question but please bear with me.

I'm about to move from an area with 6.5 tap water to an area with 7.5-7.8 (will find out when I visit the place on the weekend). My current 120L planted tank which has a leaning toward soft water species will travel with me, I've got a plan for that one and while I won't go round chasing the pH, I will make gradual changes using the current tank water and some R/O and potentially a bit of botanicals. I think I'm solid on how to manage that.

However,

In my arsenal of unused and previously used, I've got some other tanks just begging to be used, along with hardscape. Among this I've got bags of silver sand, lots of small bits of black lava rock, and a yearning to have some African dwarf cichlids - Multis etc. I can't find any reference as to how lava rock behaves in hard water - does it affect it in any way. I'm used to heavily planted tanks and not having to do a lot of water changes so this would be a bit more novel to me. I'll also be very near to a spotless water station and able to transport around 40L a week.



TLDR: What would lava rock do water with a pH of 7.5 and what would it do to RO?

Ta in advance

 

[hypnogogia]

I think lava rock is pretty inert and won’t affect your water.

 

[Maf 2500]

It is true lava rock is inert so will not affect water chemistry itself, but it is also very porous so has the capacity to bring other stuff along with it that may affect water chemistry. Depending on size of pores may have some CEC (cation exchange capacity) similar to aquasoils. If you want to absolutely ensure it will not affect water chemistry give it a few soak and drain cycles in rain or RO water.

Having said that not a big concern, especially when aiming for a hard alkaline environment for shell dwellers.

 

[ianmianmianm]

Thanks - it's been in tanks already so I hope should be good. @Maf 2500 your post reminded me that the other reason I wanted to use it was the potential for it to add a bit more biological surface area to the tank, though I don't know if that will work in the same way as live rock in a marine tank. I haven't looked properly at what the flow would need to be to enable that (I have got a spare powerhead) and whether the cichlids will like that flow. I've had a nano reef a few years back so did get very good at positioning wavemakers and outlets.