Pool has 3 suctions to a sanda filter but one of them is weak

2 on the top and 1 inside the below 10 ft of water. When trying to filter the water(skim) it seems one is working very well but other seems to be very weak. I check but nothing seems stuck or at least I am unaware of. I do not want to break the pipe and underground cement just to see. Any ideas what I can do to increase the suction power of the weak one?

Can you be more specific with what you are describing or use pictures? If you want to post photos please use a photosharing service like Photobucket to post.

It sounds like you have two skimmers and one main drain. Is that correct? If you can take pictures of what's in the pool and what the plumbing looks like at the equipment pad, it will be a lot easier for everyone to help.

To specifically address your question, it all depends on what you have for skimmers and main drains and how they are attached. Sometimes, when a pool builder installs two skimmers, they are tied together through the plumbing lines. The same can be true for a main drain and skimmer. The only way to tell is to see what is plumbed into the suction side of your pump. You can also take the skimmer baskets out of the skimmer and look to see how many holes are at the bottom. Most modern skimmers have two holes with the one towards the back being connected to the suction side of the pump and the one to the front either being dead-ended or tied to a main drain.

I doubt you have anything clogged up unless your pool was recently full of leaves and debris but, again, only with careful inspection of the setup can we help you figure it out.