Guppies Stressed by new Glowlight Danios


Hello! We introduced six glowlight danios and a bristlenose pleco into our tank yesterday and it seems to be stressing out our four male guppies. They are all hovering together in the top corner of the tank just at the surface of the water.

I'm sure the danios being so active and in the same water space is what's stressing them out. From my research and conversations with the LFS, it seemed that a strong, active group of guppies (which they have been) would get along with the glowlight danios, but I don't want the stress to make the guppies sick. How long do I wait to see if they adjust or should I just pull the danios and talk to the LFS about rehoming them?

And all the danios seem to be healthy, active and adjusting to the tank. They are moving around together in a group of six or two smaller groups. Yesterday, they were darting a lot, but today they seem to be swimming at a calmer pace. The 7 corys in the tank don't seem concerned at all about the additions. All are behaving very normal, so I'm not anticipating that they brought something in and it's an early sickness thing. I always feed the fish a little before and after new tankmates are added and the guppies all ate like normal, even after the new fish were introduced.

What is the water volume of the tank? 20G long
How long has the tank been running? 9 months
Does it have a filter? Yes
Does it have a heater? Yes
What is the water temperature? 78 degrees
What is the entire stocking of this tank? (Please list all fish and inverts.) Guppies (4 male), Cory cats (7), Mystery snails (1 adult, 12 babies - from size of pea to blueberry), Glowlight danio (6), bristlenose pleco (1)

How often do you change the water? Every week to 10 days
How much of the water do you change? 33%, 6-7 gallons
What do you use to treat your water? Prime, API Stress Coat, Seachem Alkaline Buffer (for low kH)
Do you vacuum the substrate or just the water? Vacuum half of sand substrate with water change

*Parameters - Very Important
Did you cycle your tank before adding fish? I did an in-fish cycle bc fish were gifted to us before we were able to finish the cycle, but tank has been fully cycled since April.
What do you use to test the water? Master Test Kit, plus kH and gH tests
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.
Ammonia: 0
Nitrite: 0
Nitrate: 20-30ppm
pH: 7.3

How often do you feed your fish? Every other day
How much do you feed your fish? 4 Hikari sinking wafers per feeding, Tetra freeze dried Blood worms (once a week), Vipan Nature Tropical flakes (other 2 feedings) - as much as they can eat in 2-3 minutes, steamed frozen peas - every other week
What brand of food do you feed your fish?
Do you feed frozen? No
Do you feed freeze-dried foods? Yes, the blood worms

Illness & Symptoms
How long have you had this fish? The guppies have been since April or May
How long ago did you first notice these symptoms? Last night, after the new fish were put in
In a few words, can you explain the symptoms? They are all huddled together in a group at the top of the watering, when they usually dart around and through the plants and play in the filter stream. None have clamped fins, but some are slightly bending their bodies to keep their heads against the surface of the water. One or two sometimes venture away from the group, but they seem to come back in a short time.
Have you started any treatment for the illness? No
Was your fish physically ill or injured upon purchase? No
How has its behavior and appearance changed, if at all? Just the behavior change, so far. Hoping to avoid any disease as all have been very healthy.

Thanks for any guidance you can provide!


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I couldn't see any Danios in the picture but you may need to give things more time. I know Danios are super active and this may be puzzling or intimidating to the Guppies.

Incidentally I have been keeping Zebra Danios (the wild type but I've also kept the pink Glo variety) in a 20 gallon long and they were terrific to keep alone. I didn't feel the need to mix other fish with them. They pick up all the food at all levels of the tank. Having a large number (15) meant I was free of any pecking order issues where single fish can be targeted by the others. Weaker fish could disappear into the bigger shoal and survive.


Thanks for your reply! The danios were swimming in a group behind the plants in the mid water on the left side of the tank. That's where my filter waterfalls into the tank and I intentionally left a little space there, bc the guppies have always liked to play in the moving water. That's why I'm leaning towards nerves/territorial stuff.

To your point, the guppies and corys were doing so well together that I was a bit hesitant to try another species. I think that's why I'm so jumpy about potential sickness and stress. We've tried to be very conservative with setting up this and keeping it stable, so I'm hoping it wasn't a rash decision.

The yellow and orange guppy seems to be bending his body down quite a bit, while the other three are acting much more normal and starting to venture around the tank a little more before coming back. I'm going to keep an eye on him. I also have a 3.5 gal tank that is cycled and housing the other 2/3 of the mystery snail clutch that hatched, so I could use that as a respite tank for the guppy if he doesn't seem to be perking up.

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