Can we have a planted tank with a closed top? Or do they need an open top
Yes you can have top (what ever that means to you) on your tank. I have glass tops on mine, I need to keep the glass clean or it cuts down some on the lighting.
Of course you can. There are plenty of plants that stay small. And whatever plants grow tall, all you have to do is trim them down. But there are some people that like to have open tops to let some plant grow out of the tank. It's all about what you like.
Ok one of the guy in petstore told that closed tanks are not good for planted tanks
Well I wouldn't talk to him anymore, he's not too bright.