Is shale rock not reef safe? Did it crash my friends tank?

Perpetual Novice · Nov 3, 2019

I was helping a friend of mine get into the hobby after he told me he wanted to keep a mantis shrimp. I built him a plan for his build and explained how everything works and all the “rigorous” processes and procedures he’d have to follow to set it up properly and maintain it. It’s a 13.5 gallon fluval evo marine. After 3 months a mantis shrimp and 3 clownfish had been added as well as a couple tuxedo urchins a serpent start snails and crabs.

the tank crashed catistrophically shortly after. I wasn’t there in person to help him sort things out so we had daily conversations as strange fish behavior, perplexing changes in water chemistry, and constant panics plagued his tank. He was doing water changes every day by the end and came home to find every single animal in his tank dead one day after a fresh water change that morning.

i know nothing about his tank was really done properly but he was very dedicated to putting in the work and doing all he could to follow my instructions. I figured he had overstocked and moved too fast and that it was a lesson learned.

now here is what is bothering me. When he set up the tank I told him to put a large flat rock across the bottom so that the mantis shrimp wouldn’t burrow and punch against the glass bottom of the tank. Apparently the picked a shale rock which I didn’t know.

todat he called me and told me he was changing the water again (no animals in the tank for a little while now) and had been digging deep into the 5 inch sand bed looking for any organic material... when the water started coming out black from the substrates.

I can’t give him an answer how that is possible but I think it must be the rock somehow. What else could produce a black precipitate in the water?

many ideas? Could the shale have been being broken down by bacteria and releasing waste into the water?

sfin52 · Nov 3, 2019

Shale rock holds metals and other stuff. It very well could have caused the crash and is my first suspect.

flsalty · Nov 3, 2019

5" substrate, overstocked, probably overfed? I have no doubt there was black stuff deep in the substrate.

As for the shale, shale is pretty soft. Are you sure you don't mean slate. Either way, I suppose it would depend on the actual makeup of the rock since they aren't all the same.

Perpetual Novice · Nov 3, 2019

flsalty said:
5" substrate, overstocked, probably overfed? I have no doubt there was black stuff deep in the substrate.

As for the shale, shale is pretty soft. Are you sure you don't mean slate. Either way, I suppose it would depend on the actual makeup of the rock since they aren't all the same.

yes all of the above. But the animals hadn’t been in the tank long enough to account for that amount of waste I would think. 3 weeks for a small mantis shrimp and 2 weeks for the clowns. I also don’t know why it would be black.

I normally wouldn’t have recommended him such a deep substrate but it was important for the mantis to be able to burrow. And it’s crushed coral so a little more porous than fine sand I guess.

but yeah. the circumstances don’t make it easy to distinguish what happened.

the guy has learned some tough lessons and is thinking of giving up and id like to tell him that he has now knows how to avoid this happening a second time.