Mixing Rams for upgrades

[Mehrab]

I have a 8gb ddr4 2133mghz ram. I want to get another 8gb ddr4 and make it 16gb ( dual channel ). If I can find a ram with same cas latency and voltage would it be a problem mixing the rams ? Or is it a must to buy a new set of (8gb x 2) sticks? I am a newbie in this section so any suggestions would be welcome. And budget is a issue here. I will have to sacrifice SSD if I get the new sticks of ram. So is it worth it ?

[Spirit`yL]

You can go mixing the ram you wanna input,but make sure onething that U CPU does support that two rams(i mean also they need the same working freequency),to be honest,timing is also a important thing for mixing you rams.