At the end of last season I was getting a lot of sand coming out of my returns. I knew I would have to repair my laterals. So at the start of this season I emptied all the sand from my System 3 S8S70 filter to inspect the internals. It was broken in several places and I ordered a full replace replacement for $500 from Amazon. Now I'm debating on what to refill it with. The filter takes 300lbs of sand. The brakes make me thing that the moisture left in the sand may have cause the breaks to the main pipes over the winter. The laterals look like they are being pulled downward and breaking. I'm intrigued by the filter balls but don't feel like opening it up monthly to clean them. Glass seems better than silica but is expensive. I have also read that people put pea gravel in the bottom first to help support the laterals. If I go with balls, seems like I better have the pea gravel. Should I put pea gravel if I plan on using sand? I see many good reviews on the balls but then some very adamant 'DON"T DO IT's. If I do use pea gravel, can I just go buy it at the local hardware store?
I appreciate any advice. 20k gallon inground pool (vinyl liner).
Use sand. Only sand, unless you really want to use something else more expensive, including a bed of gravel, that won't really give any benefit.
Fill the tank with water above the level of the laterals then add the sand It will flow under and surround them. From the manual:
3. To eliminate stress on laterals (Key No. 8A) fill tank half-full of water before loading sand.
4. When full, top of sand bed should be about 12-1/2” (31.75 cm) below top of distributor (about 1-1/2” (3.8 cm) below tank flange (see Figure 2).
There is no mention of gravel in the manual. Gravel is a holdover from earlier times and was used in what were called "rapid sand" filters that basically used gravity to allow the water to flow downward through the sand. They needed the gravel's less dense area for the water to get through the laterals, had a flow rate of about 5gpm so had to be incredibly large and were not pressurized. One here in town on a large City pool was literally made from an old railcar, had tons of sand in it. A friend and I were called to give a bid on replacing the sand, climbed on the top and opened the hatch with the system running the flow was so gentle, even with the 15hp pump. We passed on the job.
High-rate sand filters, like yours and what are on sand-filter installations today, don't need the gravel as the water is circulated through the sand bed and out with the filter pump.
