Early stages of disease, stress, or something else?

[GrayTeall]

Since I set my 55-gallon freshwater aquarium up about 2-3 weeks ago, I've heard occasional splashing overnight. However, yesterday and today I've caught my dalmation mollies acting strange and I suspect it may have been them that I was hearing. What inspired me to write this post was my fish ZOOMING around the tank and jumping out of the water with so much force the water sloshed in the tank. Sometimes they swim straight up or straight down, though they appear to have decent control over speed, direction, and rate of floating/sinking; they don't do it for more than a few seconds, and then return to swimming normally. As I'm writing this, the white molly appears to be relying more on momentum to move than usual. I've seen one brush against and intentionally wiggle/bump into my soft plant, but never other decorations, and she sometimes swims very erratically. She also sometimes tilts to the side for a brief moment. I also see my mollies slowly, gently glass surfing sometimes.

There are 10-13 guppies, a male demasoni cichlid, a sucking loach, a young humbug catfish, (I'm trying to rehome those three, all of my fish came from a poorly researched and unadvised community tank and anything was better than having all of them in there together), and 3 adult mollies. There's at least 2 baby mollies.

pH: 7.4
ammonia: 0
nitrite: 0
nitrate: 5ppm
kH: unknown
gH: unknown
temperature: 78 degrees

My last water change was 80% last week before my tank became fully cycled with the help of a healthy, established tank's old filter media.
The most recent addition is a centerpiece live plant that came from a healthy betta's tank, the tank had been successfully treated for ich at least 3 months prior to putting it in my own tank. I haven't put any medications in the water, but all new water is treated with prime.

 

[GrayTeall]

I forgot to add, but there are no visual symptoms of disease. Gills are a normal color, moving at a normal pace, normal colors and translucency, no unusual spots or bloating, eyes are normal, fins are intact.

 

[Colin_T]

Video of the fish movie about?

Is the sponge filter working, it doesn't appear to have air bubbles coming out of it?

--------------------
If the water quality is good then it's possibly the cichlid or another fish having a go at the mollies and they are trying to escape by jumping out of the water. The mollies appear to be hiding in the corners by the plants, which would suggest they are stressed by something.

In the picture the cichlid looks pretty small so should be causing a big issue to the mollies.

--------------------
The GH (general hardness), KH (carbonate hardness) and pH of your water supply can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).

Depending on what the GH of your water is, will determine what fish you should keep.

Angelfish, most tetras, most barbs, Bettas, gouramis, rasbora, Corydoras and small species of suckermouth catfish all occur in soft water (GH below 150ppm) and a pH below 7.0.

Livebearers (guppies, platies, swordtails, mollies), rainbowfish and goldfish occur in medium hard water with a GH around 200-250ppm and a pH above 7.0. If you have soft water and want these fishes, add some Rift Lake water conditioner to increase the GH.

If you have very hard water (GH above 300ppm) then look at African Rift Lake cichlids, or use distilled or reverse osmosis water to reduce the GH and keep fishes from softer water.

 

[GaryE]

I would suspect the Dance of the Diabolical demaisoni. Even for a nasty group of fish (mbuna), demaisoni can be rough customers.