Sudden molly die off

Never too many · Apr 3, 2023

I have a 30 gallon planted tank with 3 sponge filters powered by powerheads. I am growing Caulerpa Prolifera (which I thin out often), Halymenia Durvillei, a small ball of Chaetomorpha, and some green Gracilaria. It houses a Tiger Shrimp with a Wheeler’s Prawn Goby, 2 Blue Leg Hermit Crabs, and I was also breeding mollies. The Mollies had lived in this tank for a while and I was going on a 3rd generation. I had to move the tank, so I netted out the fish that I could easily catch, emptied the tank down to a safe level and slid the stand to its new place, and set everything back up. After a couple days, I noticed that my molly population was dwindling. A couple days later I was down to just a couple adults, who only lasted another day or two. I considered the possibility that somehow there was some cross contamination during the move, but the shrimp, goby, and crabs remained unaffected. Salinity ranges from 1.024 to 1.026. Phosphates 0.14. Nitrites and Nitrates 0 . I recently added 7 more 2nd generation mollies from one of my other tanks, only for them to die off also. From 7 to 5 to 2 to 1 over about three days. They also show no physical signs of parasites or damage. I am at a loss and would appreciate any help.

Sharkbait19 · Apr 3, 2023

Did they act off in any way? Any recent additions/changes besides the move?

Never too many · Apr 3, 2023

Sharkbait19 said:
Did they act off in any way? Any recent additions/changes besides the move?

The last one to die from the first die off was an older female that was pregnant before it started. The day before she died, I noticed that she was spending a lot of time in the plants near the bottom of the aquarium, Her breathing seemed a bit labored. No other changes or additions.

Sharkbait19 · Apr 3, 2023

It could be possible some pathogen was introduced that the mollies didn’t have a resistance to.
#fishmedic

MnFish1 · Apr 3, 2023

Yes sharkbait - or another issue - much more information is needed - suggest you click the link in my signature - and answer the question

. Sorry about the fish. There are other parameters it would be nice to know - i.e. ammonia pH. My guess is it's oxygen related. But - based on the information - with no picture of how many plants there are as compared to fish - its impossible imho to say - were you trying to establish a mollie tank = or were they just the canary in the coal mine? If so you have your answer there is a problem in the tank UNFORTUNTely. hope this helps... please give more info

Never too many · Apr 4, 2023

MnFish1 said:
Yes sharkbait - or another issue - much more information is needed - suggest you click the link in my signature - and answer the question. Sorry about the fish. There are other parameters it would be nice to know - i.e. ammonia pH. My guess is it's oxygen related. But - based on the information - with no picture of how many plants there are as compared to fish - its impossible imho to say - were you trying to establish a mollie tank = or were they just the canary in the coal mine? If so you have your answer there is a problem in the tank UNFORTUNTely. hope this helps... please give more info

The primary intention was to breed mollies. The purpose of the macro algae was to help with nutrient export, and to give the babies someplace to hide. I haven't tested for ammonia for a while because of the clarity of the water, and because it's an established tank. My pH runs a bit low, around 7.2. After I noticed that I was having an issue, I did change the direction of my powerheads to hopefully increase oxygenation. Sorry I didn't include a picture. The Caulerpa can get a bit thick, if I fail to thin it regularly.

MnFish1 · Apr 4, 2023

Never too many said:
The primary intention was to breed mollies. The purpose of the macro algae was to help with nutrient export, and to give the babies someplace to hide. I haven't tested for ammonia for a while because of the clarity of the water, and because it's an established tank. My pH runs a bit low, around 7.2. After I noticed that I was having an issue, I did change the direction of my powerheads to hopefully increase oxygenation. Sorry I didn't include a picture. The Caulerpa can get a bit thick, if I fail to thin it regularly.

Curious what was the reason for breeding mollies in salt water (that was - what I meant by my question).

PS - it would be hard - for a pH to run at 7.2 in a saltwater tank. Thats extremely low - are you sure about the measurements? If it is that low, it could be the algae is producing CO2 at night when the lights are off - do you have a constant pH meter - are you measuring pH in the Morning? If so I would suggest measuring it at PM as well

o2manyfish · Apr 4, 2023

When you set the tank back up after the move where did the water come from? If you water agency was dosing a heavy amount of chloramines, unless you have specific chloramine RO Cartridges, you might have heavily dosed chloramines to your tank.

This would explain what is happening in this tank.

The other option is, you didn't mention, if after shifting the tank you had any macroalgae die or die back. Caluerpa will instantly release everything it's collected when it goes asexual or dies. Either of which could have done a heavy instant dose of the nasties in your tank.

Dave B

Never too many · Apr 4, 2023

o2manyfish said:
When you set the tank back up after the move where did the water come from? If you water agency was dosing a heavy amount of chloramines, unless you have specific chloramine RO Cartridges, you might have heavily dosed chloramines to your tank.

This would explain what is happening in this tank.

The other option is, you didn't mention, if after shifting the tank you had any macroalgae die or die back. Caluerpa will instantly release everything it's collected when it goes asexual or dies. Either of which could have done a heavy instant dose of the nasties in your tank.

Dave B

Most of the water was the original water that I had syphoned off from the tanks (I had moved a 55 gallon reef tank at the same time). Approx 25% was water that I had made up using my normal well water that I use all the time. And no there wasn't a die back of algae. If the Caulerpa had released the nutrients, wouldn't it be showing up in my tests?

Never too many · Apr 4, 2023

MnFish1 said:
Curious what was the reason for breeding mollies in salt water (that was - what I meant by my question).

PS - it would be hard - for a pH to run at 7.2 in a saltwater tank. Thats extremely low - are you sure about the measurements? If it is that low, it could be the algae is producing CO2 at night when the lights are off - do you have a constant pH meter - are you measuring pH in the Morning? If so I would suggest measuring it at PM as well

I like having a few mollies in my tanks. They are peaceful, they make a good dither fish, and will generally help with algae control. I have also sold some back to my LFS. As for the pH, I measure it with dip strips and the the color could be between 7.2 & 7.8, there is no in-between. I usually do my testing around noon, sometimes earlier. I will run a test tonight and see what I get. I will also try a measurement with my high range test to double check.

Never too many · Apr 4, 2023

MnFish1 said:
Curious what was the reason for breeding mollies in salt water (that was - what I meant by my question).

PS - it would be hard - for a pH to run at 7.2 in a saltwater tank. Thats extremely low - are you sure about the measurements? If it is that low, it could be the algae is producing CO2 at night when the lights are off - do you have a constant pH meter - are you measuring pH in the Morning? If so I would suggest measuring it at PM as well

A 5PM pH test showed 7.8 on the dip strip and 8.3 with the high range test. I also did a ammonia test to be sure and it was 0.