I don't know if this is really an answer, but I've had a Coleman 6 person spa in service for about 25 years. Yes, 25 years! I have never had the same problems you are experiencing. We learned early on that any clothing (bathing suits etc) must be very clean and rinsed extremely well before going into the spa. Clothes cleaning detergents left in the fabrics release into the pool water and cause foam quickly. The clarifier is good at flocking these soaps, but they do tend to gum up the works quickly. We never lost a lot of pressure however, just had to clean the filter. We also made a habit of completely changing the water at least twice a year. After draining as much as we could via the drain hose, we used a wet vac to get as much out of any low spots. We then put in just enough water to cover the intake close to the bottom and jogged the pump to cycle clean water through the system and get the dirty water out. Again, drain and vacuum and repeat this process until the water looks clear. We do this with the filter out. This will clean out a lot of crap. About once a year just before we do a drain and complete cleaning, we treat the tub with anti-scale cleanser. This cleans the internal pipes of built up scale and solids. In your case, you may want to do this anti-scale treatment for a few days with the circulator on low and the filter out to purge the internal system. Then go ahead and change the water.
Another test you can do is to see how well the pump pushes water. When you have the small amount in the bottom, just above the intake, jets exposed, turn the jets to full, air off and see if the pump will shoot the water out of the jets with extreme force. Mine will shot water 20 feet away!!!! lol. If you don't have really good pressure, you may have a warn pump impeller. They can be damaged over time by chlorine based sanitizer, I never use chlorine, just bromine based shock etc.
The other item to check is if you have the right filter for your unit. Filters come in so many styles and densities. You may need to find one that allows better flow.
Assuming you find the root cause of your problem, good housekeeping, keeping as much contaminates as possible out of your tub will help. Very clean bathing suits or none at all,(yahoo) no body cosmetics such as body oils, moisturizers, perfumes etc. Keep chemical treatments to a minimum. Do a quick check weekly for PH, Total alkalinity, and bromine level. Adjust them sparingly so not to overdo any chemicals. Once you get everything under control, maintaining it is very easy and quick. Good Luck
Best Answer
You can choose to backwash and replace the DE in the filter with new material any time you want. The increasing pressure readings occur because the DE filter material fills up with dirt sucked in from the pool. There are a series of tradeoffs that you have to evaluate when deciding to back flush or not.
1) Increased pressure to pull pool water through the DE filter means that the pump motor is working harder and will pull increased current thus increasing the cost of operation.
2) More frequent backwash of the filter will incur additional cost of DE material to replace in the filter.
3) Letting the pressure build up over longer periods of time can allow excess dirt to deposit in the filter. This can lead to caking of the filter material such that it will not flush put completely when you attempt a backwash. This will generally require opening the filter unit, removing the filter screens and cleaning them with a hose. This adds significantly to the work time required to do the filter cleaning. More frequent disassembly of the filter can also lead to higher chance of damaging a filter screen and requiring its replacement.
4) Depending on the sizing of the pool pump motor on your particular installation an increased pressure load on the pump motor will raise its operating temperature. In hot summer weather this can potentially lead to motor failure if it gets too hot.
5) As you have already experienced, increased pressure due to a dirty filter, reduces flow through the pool circulation system. This can increase the amount of tine required to clean the pool if the water draw from the skimmer hose gets too low.
If your time is considered even for the various tradeoffs then it mostly becomes a tradeoff of the electrical energy costs for operating the pump at higher pressure versus the cost and availability of the fresh DE material.