HELP!! Sudden Strong Sulfur Smell in Well-Established F/W Tank

[r3blox]

Hello all, I need some help and this is my first post so I hope it’s not in the wrong area!

I have a 40 gallon breeder and the bottom line upfront is that yesterday I did a 4-gallon water change, and another today, both times vacuuming the gravel pretty thoroughly. There is a STRONG sulfur smell intoxicating the entire ground floor that came on today and lost 1 fish yesterday, 2 fish this morning (all three added in the last few days), and now have 2 more showing strong signs of imminent death, and the rest of the community gasping for air at the surface all evening today. From what I can see, nobody is dead and rotting somewhere.

Tank, Water and Inhabitants Details:

• 40-gallon breeder with glass lid
• Light runs very similar to sunup/sundown schedule
• Fluval 207 canister filter (lightly cleaned in bucket of outgoing water on a water change around Christmas)
• Water is lightly cloudy, not green by any means (slightest green tint)
• Test strips have averaged a very acidic shift, from 6.8-7.2 down to the 5.5-6.5 range over the last couple days (haven’t done full water test yet since this all developed)
• 3 total water changes in the last 24 hours: the 2 mentioned above, and then an emergency gallon tonight to rinse the filter media (50% of sponges removed and rinsed, 1 of 3 ceramic media trays rinses (and removed some to insert some tank fiber as the final stage before water flows back out)
  • Each water change is treated with combo of API Stress Coat+, API QuickStart, Seachem Prime, Pristine, or API Tap Water Treatment (not all at once, but 2-3 usually)
• Raised the output above water line for more agitation and added 4x dose of Pristine about 20 minutes prior to this post and the fish have already dispersed a bit from the surface which is a good sign
• Currently have all 4 air stones on full blast (smaller pump rated for my 20-gallon tank I ran before this that isn’t too overpowering) and the outflow filter pipe above waterline to help increase oxygenation

INHABITANTS

• 12 or so various live plants
• 15-18 ghost shrimp
• 4-5 Nerite Snails, 3 mystery snails, 3 rabbit snails
• 9-10 neon/goldfish tetras
• 1 angelfish (juvenile)
• 5 Cory catfish
• 1 bristlenose pleco
• 2 hatchetfish (1 of the guys showing signs of near death)
• 1 ADF frog
• 1 gold Chinese algae eater

Over last 12 hours, I’ve used emergency doses of pristine, prime, StressCoat+, QuickStart (most recently out of desperation), and have no ph UP until tomorrow morning to try and get the PH back up a little. Any remedies or suggestions you can think of are greatly appreciated! Also, something for that horrific sulfur smell would help, too.

[Tech Support AN]

Thanks for the post, r3blox!

I'm sorry to hear about your tank! Typically when you are getting a strong odor of sulfur coming from the tank, it means that you may have had a build up of hydrogen sulfide in your gravel and when you performed your water change along with a gravel vacuum, you released the gas into the aquarium. Unfortunately, hydrogen sulfide can be toxic to inhabitants. It also looks as if you have a slight algae bloom in the water.

I would recommend keeping the water well oxygenated (as you have already done), ensuring there is a lot of surface agitation. I would add some of our MatrixCarbon into the filter to assist in removing any residual hydrogen sulfide from the water. Going forward, you will want to ensure that you keep your gravel clean by doing routine maintenance on it so that it does not become anoxic in certain areas i.e. under rocks or other decorations, as this is what causes a buildup or pockets of hydrogen sulfide. Adding Pristine routinely will also assist in breaking down any organics in the gravel that could lead to this issue. I would also keep an eye on your parameters, ammonia, nitrite, nitrate and phosphate.

I hope this helps! Let us know if you have any further questions!