[jellopuddinpop]

I’m planning out my new tank, and I’ll be using a pretty coarse layer of lava rock granules as the base layer in the substrate(.500-.750" pieces). The reasoning for this is to add more surface area for biological filtration, and to add height without having an anaerobic layer. My question is this… How thick can I reasonably go before I risk anaerobic respiration at the bottom? In case it’s important, this is going in a 125G tank, and I would really like places with the substrate 10-12” thick (7-9” of lava rock + 3” of BDBS). Will this work out fine, or am I asking for trouble here?

 

[Oughtsix]

In my experience you should be fine. The deepest substrate in my tank is about 8" (6" of soil and 2" of gravel cap). It has been running for 5 years now and it has never been an issue. It did let off a lot of bubbles the first 6 months but careful monitoring (sniffing) revealed no detectable signs of rotten egg smell.

I will be using up to 8" of soil with a 2" gravel cap without any concern in our new 180g tank. I would have no worries going thicker if I cared to.