Fish dying at once, but corals still ok

[grumpy47]

The tank has now been set up 7 months. Yes, we have a glass top, but the Fluval 307 filter, which we clean every 4 months as recommended. We have a wave runner to push water movement at the surface And a second unit to create movement around the corals.
we keep the tank at 76 using a cooler, if we didn’t have that - it would be around 80.
no stinging when we touch the water.
we use city water filtered thru an osmosis unit for water changes and also add Prime.
we have a refractor and hydrometer and use both to check the salt levels.
Thinking back, he might not have given the water he added enough time to reach the same temp as the tank. maybe That’s the problem? I do remember the first time it happened, was a day he had to work. But, if he did the water change on Sunday - it could’ve been Monday morning. Needless to say, he had a crappy work day.
He did water changes every week at first, then switched to every 2 weeks this past month. guess in the future, he should let it sit in the bucket overnight to warm up to room temp. In our case, that’s 76...

Just texted our grandson with your suggestions. He said the water temp & salt may be our problem. He just Said he puts a spare heater in his 5 gallon bucket to bring the water temp up and a wave maker to make sure the salt is mixed well. We hadn’t been doing that.
expensive lesson to learn...

 

[grumpy47]

The tank has now been set up 7 months. Yes, we have a glass top, but the Fluval 307 filter, which we clean every 4 months as recommended. We have a wave runner to push water movement at the surface And a second unit to create movement around the corals.
we keep the tank at 76 using a cooler, if we didn’t have that - it would be around 80.
no stinging when we touch the water.
we use city water filtered thru an osmosis unit for water changes and also add Prime.
we have a refractor and hydrometer and use both to check the salt levels.
Thinking back, he might not have given the water he added enough time to reach the same temp as the tank. maybe That’s the problem? I do remember the first time it happened, was a day he had to work. But, if he did the water change on Sunday - it could’ve been Monday morning. Needless to say, he had a crappy work day.
He did water changes every week at first, then switched to every 2 weeks this past month. guess in the future, he should let it sit in the bucket overnight to warm up to room temp. In our case, that’s 76...

 

[DanTheReefer]

Just texted our grandson with your suggestions. He said the water temp & salt may be our problem. He just Said he puts a spare heater in his 5 gallon bucket to bring the water temp up and a wave maker to make sure the salt is mixed well. We hadn’t been doing that.
expensive lesson to learn...

Great hopefully that’s the issue because it’s a lot easier to correct for than anything else. It makes sense that the coral would be alive while the fish died. While more sensitive to water chemistry overall, coral does seem to handle infrequent sudden changes a lot better whereas the fish can go into sudden shock and die.

I’d say keep going slow and QT new additions. Still may want to be fallow a few weeks. If you can’t QT I’d consider the online vendors who specialize in providing disease-free fish such as Marine Collectors or Quarantined Marine. You’ll pay probably 2-3X as much but every fish you add is helping avoid the $400 loss of an entire tank you just went through. Good luck!

 

[Lasse]

I understand - no skimmer and suddenly healthy fish die during one night? Glass cover? Heavy feeding? Whit what?

Oxygen:
Do you have good water turnover? Is it a glass top with a hang on back filter? Probably still unlikely in that case but still something to consider

IMO - spot on but I think this i likely the cause of your problems. There is a chance that your decorations is the cause too - but IMO - your corals should have reacted if there was toxic compounds in them. But take them out.

Oxygen depletion or/and forming of hydrogen sulphide are IMO the cause. Especially when you are low in nitrate. Did you sense any smell of rotten eggs?

Sincerely Lasse

 

[grumpy47]

I understand - no skimmer and suddenly healthy fish die during one night? Glass cover? Heavy feeding? Whit what?


IMO - spot on but I think this i likely the cause of your problems. There is a chance that your decorations is the cause too - but IMO - your corals should have reacted if there was toxic compounds in them. But take them out.

Oxygen depletion or/and forming of hydrogen sulphide are IMO the cause. Especially when you are low in nitrate. Did you sense any smell of rotten eggs?

Sincerely Lasse

The corals turned from green to brown. They do have green buds and are starting to open up again. It’s been a week since the fish died and we took the plants & decorations out of the tank 5 days ago.. we wondered about the oxygen, the first time all the fish died. Both wave machines were aimed at the corals - so we positioned one to make waves at the surface. We do have a skimmer.

 

[ZoixDark]

if you have a skimmer there's way more gas exchange there than anywhere else in the tank so you wouldn't have a lack of gas exchange though if you have a lot of CO2 in your place then, who knows.

As far as API test kits being so bad, I tested tank water, RO, fresh made saltwater, and distilled water and they all tested exactly the same for the kit I was using which would be impossible.

 

[Lasse]

We do have a skimmer.

Can you post a picture of the skimmer and where it is placed and where the air is taken from?

Sincerely Lasse