Lava rock for sump

[Midwater]

Lava rock probably has a great internal surface area, but that doesn't matter when it comes to filtration.
Water flows where resistance is lowest — around the media, not through it. In most cases, it's the external surface of the media that matters.
For example, PVC shavings are more effective than Siporax. [See: https://www.docdroid.net/wLLOb91/siporax-pdf]
All ceramic media are inefficient — 4 to 6 times less effective compared to K1 or foam.
Additionally, lava dust can shorten pump lifespan.

Each to his own.

 

[robert_gorajski]

T triamond - thank you very much for sharing that PDF study.
It was a really insightful document for me, especially the part discussing the fluctuations in pH levels. I've observed similarly strong pH swings in my own system, and reading this helped me better understand what's happening. Now I see that only minor adjustments are needed on my end to stabilize things further.

 

[robert_gorajski]

Where do these reputable online stores buy it from?

Post some pictures of your setup.

Midwater – apologies for the delay!
As requested, here's my filter setup, which I posted earlier on the forum.
https://www.monsterfishkeepers.com/forums/threads/bigger-filter-than-the-fx6.764753/post-8576352
I forgot to mention in that post: one of the boxes contains lava rock.
So for biological filtration, I’m running a mix of Sera Siporax and lava.