Hell no. I was debating whether or not I should put him in the tank with three large reds or put him in one by himself. I decided it was not worth the risk, so he is currently in a 29 gallon tank. I'll put him in the big tank once he hits six inches.
you will probaly see a lot more of the colour after a couple of day as i did with mine possibly due to getting used to the new tank and water in it .it was still nice colour when it arrived but is amazing now .
good luck with the new piraya good choice adding it to the other tank thats what i would have done if i did not sell my 8'' + reds before getting it