In a saltwater tank when a diamond goby digs up the deep sand bed (DSB). November 2015
A customer recently lost all things alive in his aquarium after adding a diamond goby with a 4” DSB. The goby went to work cleaning the surface aragonite (sand) with no affect. The problem started when he began to dig burrows under the rocks below the 1” aerobic layer.Hydrogen Sulfide (H2S) began using oxygen faster than it could be replaced. He didn’t have a protein skimmer but because H2S removes oxygen faster than a skimmer can put it back in, the same result happens.
The percentage of each of these species that is formed depends on the salinity, the pH and the temperature, but the predominant product is typically sulfate [SO4-2].
H2S + O2 → [SO4-2; SO3-2; –SSO3 -2 ]
The use of a plenum ( Aquarium Setup ) prevents H2S formation and no harm should a goby uncovered it.
Hydrogen sulfide is considered a broad-spectrum poison, meaning that it can poison several different systems in the body, although the nervous system is most affected.
The toxicity of H2S is comparable with that of carbon monoxide CO
• 0.00047 ppm or 0.47 ppb is the odor threshold, the point at which 50% of a
human panel can detect the presence of an odor without being able to identify
• 10 ppm is the OSHA permissible exposure limit (PEL) (8 hour time-weighted
•10–20 ppm is the borderline concentration for eye irritation.
• 20 ppm is the acceptable ceiling concentration established by OSHA.
• 50 ppm is the acceptable maximum peak above the ceiling concentration for an 8-hour shift, with a maximum duration of 10 minutes.
• 50–100 ppm leads to eye damage.
• At 100–150 ppm the olfactory nerve is paralyzed after a few inhalations, and the
sense of smell disappears, often together with awareness of danger.
• 320–530 ppm leads to pulmonary edema with the possibility of death.
• 530–1000 ppm causes strong stimulation of the central nervous system and rapid breathing, leading to loss of breathing.
• 800 ppm is the lethal concentration for 50% of humans for 5 minutes exposure
• Concentrations over 1000 ppm cause immediate collapse with loss of breathing,
even after inhalation of a single breath.
Short-term, high-level exposure can induce immediate collapse, with loss of breathing and a high probability of death.
Loss of Oxygen
A real occurrence 11-27-15
Fish dying over several hours
Fish dying like this can happen in only 3 ways  external contamination – not likely but something to consider  pH shock – your procedure is great  suffocation – this is most likely having seen it happen in 30 years of saltwater. I’m going to guess this is what happened. For some reason the oxygen level wasn’t as high as it could be. Protein skimmer off? Not enough surface motion. Besides increasing oxygen you have to degas carbon dioxide. Next you added 8 fish – not recommended but I’ve added 40 fish to 200 gallons in my aquarium shop many times. I recommend salinity around 1.023-1.024. The south pacific is 1.022. As salinity increases (1.028) fish find it harder to breath. It also becomes harder to increase oxygen and carbon dioxide will not decrease as easily. When the fish went into the tank more oxygen was being used then replaced and you witnessed the results (of fish dying over several hours). It was more than one thing that happened.
Still seeking an explanation 12/15/15
I have 2 Caribbean condylactis anemones that turned totally white except for their mouths which remained red. Their living conditions were “harsh” for a while. They were present while the tank was treated with a double dose of Flatworm Exit for 12 hours, two 90% water changes and then treated with a probiotic detritus cleaner from Tropical Science. The first anemone was out of water about 20 minutes while aiptasia was being removed from its rock. The anemone went back into the tank. The anemone regained its purple colors in about 2 days.
There was a second anemone in the same condition. We repeated the steps. The second also regained its colors. I’m hoping to find out why this happened and I’ll post it here when I do.