Aggression In Platies

In my 110 liter tank I have 4 male platies. 2 reg wagtail platies and two red sunset platies. The red sunset platies are bigger in size and from yesterday they are fighting. Yesterday after feeding them one of sunset platies was nipping on second platy and they were literally twisting and rotating their bodies while fighting. After a few minutes I captured the atttacker in net and left him in for 10-15 minutes. Then I released him. After that they were fine for a while but much scared of me and hiding under plants. I put 10,12 more plastic plants in and bit rearranged the other deco in ordee to solve any territory issue. Today morning when I turn on the light I found the victI'm fish's uper fin is ripped. It's damage in two different spots. I tried to catch attacker but as other fish were sacred too so I left it. Now all platies are hiding and look scared of me. Normaly they trust me and often I feed them with hand. What should I do to stop them fighting? What can be the reason behind aggression?
My tank is cycled.
0 ammonia/nitrite
30-35 nitrate (25 nitrate in tap water)
Ph 7.6-7.4
Temp 25 degrees Celsius
Would be thankful for any help

 

Boys will be boys, and they will argue often. How long have you had them? They might be working on the pecking order still, trying to figure out who's boss. If there is enough room, you can try adding a few more males, this way the aggression can be spread out a bit more. If the aggression continues then I would see about re-homing the aggressor (if it's the same one each time).

 

What can be the reason behind aggression?

they're all males... platies are best kept as trios 1 male 2 females, this keeps them from exhausting females with prolific breeding, and keeps their aggression at bay.

Males will fight. Especially in that small of an area. Without females to keep them busy, they will fight, and most likely kill each other. The dominant male will certainly harass the less dominant males until they die of exhaustion, or wounds.

 

If I get 4 female platies will they still fight? Will they eat all of their fry?

 

4 females won't cut it, you will need 2-3 per male. That would mean you will need at least 8+ females. You want enough females to distract the males and keep the stress on females to a minimum. Any fry they produce will most likely be eaten or sucked up the filter. A few might survive if there are hiding places, then again you might become over run with surviving fry.

I still think raising the number of male platties would help. I know this won't work with with species like bettas and gouramis, but if you over stock an all male African Cichlid tank, there will be less picking on any single fish = aggression is spread out. This works for the more aggressive barbs/tetras, betta sororities, mollies etc. I think you should give it a try.