That really depends on how blue you want the tank.And what K MH bulbs you have.
Like in my situation,if I was running 2 Phoenix 14 K actinic supplementation wouldn't really be a big deal.
Just use it for dusk/dawn effect.
But If I had say 2 Ushio 14K or a bulb that is more white 10k.Then yes,I would go with 2 or double actinic.