Leopard Danios Dying Quickly!

[StickySwamp]

On Tuesday, Feb 4, 2025, my husband and I set up a 55-gallon tank and we were recommended to use 6 leopard danios to do fish-in cycling. The tank has a soil bottom with a sand and pebble cap and has 14 plants throughout along with one piece of aquarium decor (a ship). When we acclimated the 6 leopard danios, we let the bag float on the surface for 10 minutes and over the next 30 minutes added a cup of water from the tank into their bag in 10-minute increments. After that, we netted the fish and added them to the tank where they primarily stuck to the top and were gasping for air. We chalked this up to being stress-induced because no ammonia, nitrates, nitrites, or chlorine were present, the water had a pH of 6, and the temperature was at 70. The next day they began to explore a little more but still came up to the top for air. They were also responsive to food, and we have been cautious not to overfeed or underfeed them. This behavior continued but then they began to slow down which was concerning because the pet store we went to warned us that these were a type of fish that never slowed down. On Thursday morning I woke up to one of our fish dead at the bottom of our tank. I immediately contacted the pet store via Facebook and explained what had been happening and they said that the pH was too low and that it needed to be brought up and the water temperature could rise as well. While also doing research we discovered that they could benefit from some more oxygen in the water. That day I bought a bubbler and heater for the tank and have been raising the pH by .2 every day. The fish began to perk up and get their energy back so I was hopeful, but today I woke up to one of our fish nearly dead with the rest of them happily exploring the tank. I checked the pH and temperature and the pH seemed to be on a steady gradual incline at about 6.4 and the temperature was a nice 74. I left for work hoping he would pull through but when my husband arrived home from work this morning about 3 hours after I had left he came home to two more of our fish dead at the bottom of the tank. Now we have 1 fish doing amazing but the other two are hovering near the bottom gasping for air looking like they don't have much time left. The unhealthy fish at the bottom have started to become a more orangey color whereas the happy and healthy fish has not changed. I have been checking the ammonia, nitrites, and nitrates every day and all are at 0ppm and today I noticed the slightest rise in nitrate but not enough even to consider it as 5ppm. If there is a rise in nitrates wouldn't that mean the tank is beginning to cycle?? My husband and I are at a loss for what to do now because it seems like as much as we are caring for these fish it does not seem to be enough. If anyone could give any advice or explanation as to what's going on much would be appreciated. Also, will they be okay with only 3 of them in a 55-gallon tank, maybe turning to be 1 if these poor guys don't pull through? I have read that they're happiest in groups but I would hate to add more to the tank if they are going to be met by the same unfortunate fate.

Extra info:
-We are feeding them shrimp flakes
-We used water conditioner before they ever entered
-The pet store recommended using FRITZZyme Turbo Start Freshwater 700 the 1fl oz. bottle. They recommend dosing 1/3 of the solution before they enter the tank, 1/3 of the solution 3-4 days after they're in, and then the last third after a week of them being in there. The bottle says to use the whole thing in one dose for a 50-gallon tank and with our fish only getting worse we ended up using the remaining 2/3 today because we were beginning not to trust the recommendations we were given and were planning to rely on the bottle.

 

[Andy Sager]

The store was definitely correct that a pH of 6.0 is too low for Danios but unfortunately, a pH that low will not support a healthy biological filter. Nitrification slows under the 7.0 and the lower it goes, the slower the process until you reach under 6.0 where it eventually actually stops happening so the Fritzyme was a waste of money in your case.
Regarding your fish, it sounds like the fish had a lack of oxygen when you were bag acclimating OR something is in the water maybe coming from your soil substrate so it effected the fish more in the bag. That turning orange color is a clue to bad water quality. Definitely do not add more fish until this is settled.
The slight rise in nitrates can be coming from your substrate or fertilizers for the plants as much as it was just a misreading on your part.
This is a picture of the nitrogen cycle in graph form. As you can see, you can't have nitrates naturally until you have the 2 microbes, ( 1 that converts ammonia to nitrite and the other to convert nitrite to nitrate). 6 small fish in a larger tank like a 55 will not produce enough ammonia in 3 days to effectively create nitrates.
So now the questions:
What kind of filtration do you have on the tank?
Have you tested your source water ( Tap water I assume) to compare it to what's now in the tank?
Can you post pictures or a video of the tank and fish in action so we can see what's going on?

 

[StickySwamp]

Thank you so much for your help. I don't have the box anymore for our filter, but the brand is Imagitarium and it looks like the picture attached however it is rated for a 55-gallon tank. I have videos from when they were first introduced to the tank and how they are now, but it will not allow me to upload them. Is there another way to share videos here? I gathered readings from before we started adding to the fish tank and all came back normal however the pH was quite low, sitting at 6.
How quickly would you recommend raising the pH?

 

[CfishGo]

Did you use a water conditioner/declorinator when you filled your aquarium? I'm sorry for asking if you already said you did I must have missed that part.

 

[StickySwamp]

No worries! And yes, I did, I also tested to confirm before they went into the tank and no chlorine was present.

 

[Andy Sager]

For videos, you need to upload them to another site like Youtube or Imgur or the like then post the link to your videos in your posts. You can load pictures here but not videos directly.

Filters are a funny thing. Most are rated " up to" a certain size and it seems that only works when they are new or have nothing in the filter that could slow down the flow rate. You really want a filter that is rated for higher than your tank size vs the high end of their " up to" range. So for your tank, a 55 gallon, you really should have gotten something rated for up to 70-90 gallons. Since you are using an internal filter, how much is your filter breaking the surface of the water?

As for raising the pH, you are doing it correctly. You don't want to raise it more than .2 in a 12 hour period.

 

[StickySwamp]

I'll work on getting those videos uploaded! With the pH steadily increasing they are doing much better! The two on their last legs are now getting their color back and zooming happily around the tank. One thing that has changed is that it seems like one of the fish has now taken it upon herself to bully her mates. I do not see any damage to the other fish's fins; however, I see the female chasing the other two around trying to nip at them. The two being bullied were originally the two not doing so well.

Also thank you so much for the filter explanation. I'll find the box for the filter and see if we need an upgrade.

 

[Andy Sager]

Are you sure the bully is a female?

 

[StickySwamp]

I believe so, but I could be wrong. Of the three leopard danios we have two have rounder bellies and the third is slimmer. Attached is a picture of them.

 

[Andy Sager]

The fish in pic 1 is more likely a Male but really needs more meat on it to be sure. In the pic of the 2 fish, the upper fish is definitely a female but the bottom one could just be a well fed male or a maturing female. If the fish in pic 1 was the bully, it is definitely a male and the chasing of the female(s) is normal behavior.

 

[StickySwamp]

The bully is the top fish in the second picture, the one you said is definitely a female. What would cause her to bully the others?

 

[Andy Sager]

The bully is the top fish in the second picture, the one you said is definitely a female. What would cause her to bully the others?

Checking for a mate or possibly a rival for a mate. Healthy fish will also peck at unhealthy fish with the intention of eating them because sick fish are easier to kill and eat than healthy ones are. That's the " law of the sea", survival of the fittest.

 

[StickySwamp]

Is there any way I could help if she is trying to kill the other fish or since it's the "law of the sea" do I just let nature take its course? When the two fish were unwell she left them alone, but now that they are doing better and look healthier her pecking behavior has started. Does that mean it's some sort of mating situation or could it be residual "feelings" from when the other two were unwell?

 

[Andy Sager]

Is there any way I could help if she is trying to kill the other fish or since it's the "law of the sea" do I just let nature take its course? When the two fish were unwell she left them alone, but now that they are doing better and look healthier her pecking behavior has started. Does that mean it's some sort of mating situation or could it be residual "feelings" from when the other two were unwell?

It would be best for now if you could separate her from the other fish. Either use a tank divider or a separate tank. I wouldn't try using anything small like a Guppy breeder tank or net breeder as Danios need to swim.
Her reasonings are not clear because usually males push the females into a spawning site ( usually the gravel or a plant patch), not the other way around. This is why it points towards a survival issue more than a spawning issue but nothing is 100% at this point. When the other 2 fish are stronger and have gained back whatever weight they may have lost, putting the female back with them will make it a " fair fight" vs what's happening now.