Male dwarf gourami goes crazy when the light is turned off

[Ategnatos]

I have a 20-gallon aquarium and about a week ago I bought two dwarf gouramis, one male and one female. I have noticed the last 3-4 days that when I turn off the aquarium light the male gurami goes crazy. He starts swimming erratically and making sudden movements and seems very paranoid. For some weird reason as soon as the light is off, he also starts to tilt on one side (either right or left). About 30 minutes to an hour later he calms down. The female one on the other hand seems to be just fine. Is the behavior of the male gourami expected or should I be worried? I want to note that I am not making the aquarium go from full brightness to total darkness. At morning I let the sunlight illuminate the aquarium for a couple of hours, then turn on the aquarium light for about 12 hours, switch it off at late evening while leaving the room light on and finally at night switch off the room light too.

[Arget]

Since the room light is still on, he could be seeing his reflection. Male Dwarf Gouramis are a lot like a male Betta, but not quite as aggressive. He could be seeing his reflection as a rival male, and they get even more aggressive to other males if there's a female. Is the tank planted? 12 hours of light can be a lot, and can lead to uncontrollable algae growth.

[Ategnatos]

You are probably right his reflection is probably what's getting him riled up. Anything I can do about that? Also, the tank has no real plants so should I reduce the hours the light is on?

[Arget]

Definitely. A non planted tank only needs about 6-8 hours of light a day. The more light, the worse the algae can be. Planted tanks need about 8-10 hours of light per day, and it can decrease algae, since the plants take up all of the nutrients from the algae. I've had a 10" female Red Oscar act the exact same way, and the light was a fancy one that had a built in timer and dimmer. The reflection thing, you can't really do anything about it since you use the room light. The only thing I can think of to prevent it, would be to put a blanket or towel over the tank before you shut off the lights. That way it can prevent the room light from causing reflections and getting him riled up. Having plenty of hiding places can also help, floating plants in particular. According to my LFS, the males use floating plants as territory, and I've seen them build really good bubble nests with floating decor. You might also want to watch them pretty carefully, they can get a bit mean when defending the nest. I'm not sure if you need to remove the female after spawning like you do with a Betta though. I've got two males of my own in a planted 55g, with some floating decor.

[Peartree]

Hi i had the same and i was able to adjust my light so it would automatically turn down bit by bit till it went out i got it from amazon for about £40 it might be worth looking into otherwise put in some floating plants in (dwarf lettuce) as they like to sit underneath and will even make a bubble nest under it i hope this helps cheers Paul

[Colin_T]

How long has the tank been set up for?
Can you post some pictures of the fish and tank?
Can you post a video of the fish freaking out?

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It's normally caused by the stress of going from a brightly lit aquarium to a dark one instantly. If you add some floating plants to the tank, they will shade the fish and there will be less stress on them when the lights come on and go off.

Water Sprite (Ceratopteris thalictroides/ cornuta) is one of the best floating plants for aquariums. If it grows to well, you can plant the surplus plants in the gravel.

Gouramis and Bettas need floating plants so try to get some asap.

You should also check the water quality for pH, ammonia, nitrite & nitrate.

In the mean time, do a 75% water change and gravel clean the substrate. this will reduce the chance of the issue being caused by poor water quality.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

[Ategnatos]

Thanks for your advice I will look into getting some floating plants. Turns out the user above was correct it was indeed his reflection that was riling him up. I covered the aquarium with a shirt when I turned off the light and he was fine. As soon as I removed the shirt he was startled and started becoming kinda aggressive on the glass in the front. I covered the aquarium again and he relaxed once more, so I am pretty sure it's his reflection that's riling him up.