I generally agree with your
LFS that terrestrial/mined rock (of any sort) can be problematic.
A few points:
- A lot of mined "lace rock" marketed for cichlid tanks is, in fact,
calcareous.
- Any time you use dry rock (lace/base/whatever) you will see "invasive" species colonize quickly because, well, they're called "invasive" for a reason! Dry rock has absolutely nothing - not even bacteria - on it or inside it.
- Porous is Porous. Denitrifying bacteria will colonize anywhere the oxygen level is low and could care less if that was inside
live rock, lace rock, base rock, fake rock, your sandbed, or the bottom of your kitchen garbage bag. Almost all
nitrate reduction in a reef tank happens in the sandbed, not the rocks.
- Hydrogen sulfide in your rocks or sandbed is generally due to insufficient water flow (specifically: denitrifying bacteria are not getting enough nitrogen). This could be partially due to not rinsing/cleaning the lace rock well enough before placing it in the tank - limestone sedimentation and dust can clog up dry rock quite quickly.
So, if the pores in the rock seem "clogged" then the rock probably wasn't rinsed/cleaned well enough before being placed it in the tank... which means it also wouldn't have been washed well enough to remove any potential contaminants in the rock/dust - which could very well be a factor in your algae issue. Try the old "turkey baster in the hole" trick and see how much sediment you can blow out and let it settle to the bottom of whatever container you've got the rock in. Collect and examine the sediment in a smaller container (clear shallow bowl or petri dish) and see if you notice anything that doesn't look like sand.
