water stats are all good , i am hopin to keep those fish in the tank for ever , most of them are smallish at the moment but will this tank be suitable for them when they are fullly grown ?
You need to say which type of plec it is as some grow massive.
Silver sharks, bala shark need to really be in a bigger group, probably need a bigger tank if you bought more of them.
If your stats are ok then no. What filter do you have in there?
As a guide for stocking head over to http/www.thinkfish.co.uk/. Go to community creator and enter your tank dimensions etc.
Silver sharks like to be kept in a group of 3 or more, however, I've got two and they like to shoal and swim with my Torpedo Barbs so you could be ok. Depends on the fish really. They will get pretty big too - but in a 400l you'll have more than enough room. What kind of Plec do you have, the Common Plec gets HUGE.....