Bacterial blooms unfortunately usually go undetected. It is caused from lack of oxygen in the substrate caused from crabs burying food, and other natural items that decompose underground. The substrate will smell really bad when dug up. Rotten eggs, musty basement, ammonia, to name a few smells. Mine was a dark grey color too. If it's in the center of the tank you will not be able to detect anything.
This is more to check for laying water rather than a bacterial bloom. If you have one it doesn't mean you have the other but there is a good possibility. Slide a butter knife of something down the front glass all the way to the bottom of the tank. Give it a wiggle or two and pull it out. If you have laying water at the bottom the water will pool in that hole. If you have any laying water you will need to get that out. I tried to soak up the water with towels in a few holes. It worked to lower the water table but didn't help with
Either one pretty much requires a complete teardown and rebuild. Some people will salvage the good substrate and reuse it. We opted to just start from scratch just to be safe.
Our floods came from our bubblers over spraying onto the substrate over a 5-6 month period. If you are loosing a lot of water between water changes it is going someplace. A lot of people put dry moss around their pools to help absorb overspray. Then you can swap that out with stuff that dries in the moss pit!
A few searches for tank flooding or bacterial bloom should bring up a few posts.
Hopefully that helps. There is also mention of Bacterial Blooms and Flooding in our Substrate Care Guide.
viewtopic.php?f=26&t=92542
I was hoping he would make it.
