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
I have this exact same problem. The only option I have found is to use a chemical additive to precipitate out the the iron and then do lots of filter cartridge changes. Luckily, the cartridges don't seem to be deteriorated by the orange stuff, and you can just swap two of them every 12 hours and wash them off with the garden hose. If you have a full size filter, you will just need to do a backwash every day or two.
It also helps to get in the pool and stir up all the precipitate off the bottom so that it can be captured by the filter...there's nothing in there that will harm you, it's just orange.
Best Answer
It depends on which model and what rate of flow you are using at the time. The manufacturer's spec sheet has the details:
Big Blue Filter Specs
See the section titled
In the table there look at the right-hand column for INITIAL ∆P. Also refer to the graph: PRESSURE DROP VS FLOW RATE
EDIT:
In your comment you said:
No, you asked about pressure not flow rate. Specifically you asked:
This is answered by the specs from the filter manufacturer. This does not address flow rate as that is NOT determined by the filter.
To specifically answer the questions you raised in your post as well as the question you asked in your comments:
Check the specs on your pump (assuming you have a pump as you didn't say) and you will see graphs such as this one that show how the pump's flow is affected by the pressure (i.e. the "head").
Sample Flow vs. Head Graph
In other words, it depends.