Help Guppies aggressive unless the blue light is on?


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Hello everyone!
I'm writing here because I'm really bothered by my guppies' behaviour.
We've only got the fish tank and all our fish very recently, so I'm not experienced at all and was hoping that someone would be able to help and maybe explain the guppies' behaviour since I couldn't find any thread discussing a similar issue.
The culprits and main figures of this problem are three male guppies that we have, which have been harrassing our male platy for quite some time. In the beginning everone seemed to be getting along fine and the guppies used to keep random fish company, but then out of sudden all of them started nipping and chasing the poor thing. I've read somewhere that some guppies are just meanies for the sake of it? But I'd very much like to help the poor platy somehow, because they're constantly bothering him.
Can anyone please give me any advice on this issue? Do I just need to get rid of the guppies? All the other fish are doing fine and there are no conflicts that I know of.

The second problem/mystery is the temporary solution i've found for this issue. I've randomly noticed that the guppies don't, or only very rarely, pick on the platy if the blue light is on. I have no idea why, but if there's normal lightning on, or if they only get the natural light from windows, they will start chasing him and biting. However, this immediately stops when the blue light is on, which makes me use that one only for the platy's sake. Is this a bad temporary solution?(Until we'll get some plants in so that the platy has more places to hide from them?) And, why does this work at all?

Thanks in advance to anyone taking the time to read this!


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Closer to Heaven every day but for now-Arkansas
More than 10 years
I can't see it being a bad idea. As to why it works. I can only guess. It must have something to do with how they see colors. In normal daylight or any other color of light the guppies see the platy as the enemy but the blue light changes its color and it no long poses a threat to them.

Lots of things to break line of sight often helps so you may want to add the plants sooner rather than later.

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