I have a 1000 gal septic tank thats about 10 years old. I have it pumped about every 3 years. I picked up a drawing and plat map from the county which shows its a 150' single chamber drain line.
Problem: This past year its backed up a number of times, makes gurgling sounds, and I've had to pump it twice in the past 6 months. There havent been any obvious reasons for the drain failure other than maybe more water usage than previously. With teenage kids, the washing machine and/or showers seems to run constantly.
I dont have any soft spots in the yard near the drain field or anywhere along where the drain line runs.

Septic Co says I need to add another 50' to the chamber. They didnt scope the line or anything...just said to add on to fix the problem. Is there a way to trouble shoot this to get a better idea of the cause?
Ive read about Biomat...Is this a possible issue? Are the commercial shock products (NT-Max, Biosafe-One, etc.) effective at all?
Any ideas on how to definitely trouble shoot the problem?

If the line has failed due to putting too much water thru it this past year or from solids blocking it, what is the best course of action to fix this? Are there any fixes short of replacing drain field or adding to it?

Any knowledgeable suggestions or information would really be appreciated.