Our newly installed sand sand filter septic system smells terrible. What can we do to stop the smell.?

We installed this system to the T by the county dept requir 1 yr ago. We don't have a pump system at the end of the septic tank as I have read that others have. Our pipe is 6 foot above our roof. Do we need more lenghth there? The ground isn't saturated anywhere that I can tell. I put a bacteria disk down the toilet 1x a week to help with decomposition. Sometimes the smell is so bad it takes your head off. The smell comes from the pipe over the roof line and also from the vent pipe over the drainage fields. I keep chlorine tabs down the chlorine tank, (last tank) as we are supposed to before the water comes to surface. It doesn't seem to stink at the water run out area. Just from the pipe over the roof and from the vent over the drainfields. It almost seems like we have alot of draft that runs through system from the vent pipe. I have even put plastic over this to stop the draft. Not sure if I am hurting anything by clogging off air flow, but just desperate to stop this smell