I have a fish pond (approx 2000 gallons) that came with the house I just purchased. It went green so I asked 2 local companies for advice. Both came to the house and looked at my pond. The filter is a biological gravity filter by the way. One guy said don't touch the filter and the other one said clean it out down to the laval rocks every 4 or five days.
I am confused. My reading on the web seems to indicate that biological filters should not be touched. Is this correct? Do I at least need to clean off the top spongy pads every now and then? If so how often? Any advice would be appreciated. I am determined to learn about this pond and get it right. Thanks.

The green is algae. There are products you can use to treat this.
Algae Destroyer Pond is one of them and you can find it, or products like it,
At any pond supply store.

If it is a biological filter then it's best to be left alone.
You can however, and only if it's all gunked up, shake off debris
From the spongy pads in the pond.
Put the pad under the pond water and give it a good shake then put it back in the filter.
Lots of beneficial bacteria live on those pads and you don't want to remove
Them from the pond because they are what keeps the water clean.

You may want to think about a mechanical filter with UV clarifiers that will keep your water clean from debris and algae.

Good Luck.