I've just got back from another visit to the house and submitted another sample for testing. It seems that everything has changed and those saying the pH problem would eventually self correct are absolutely right! The latest pH reading is 7.8. However this pH correction comes with a huge increase in iron level - up to 0.344 mg/l (up from 0.068 mg/l) and a rise in turbidity to 2.7 NTU from 0.6 NTU. So my pH problem is solved but I'm back to square one with the iron problem. This is exactly the same issue I had with the old Triplex media.
I'm wondering if it's all due to the backwash problem. My rate is approx between 9 - 6 g/min/sq ft instead of 10 - 8g/min/sq ft. Whereas I can see that the backwash rate might delay the dissolving/flushing of fines, I wouldn't have thought this would result in serious clogging of the media. If it does then will the media be "cleaned" by more vigorous backwashes or is it clogged for life!
If it's not all to do with the backwash then could the rise in iron level be due to the lowering in pH and the excellent iron removal earlier was due to the very high pH of 9.8. In which case am I now looking at how to raise the pH rather than lower it!!!
I suspect it is the Fleck 2750 controller that is the main limiting factor in the backwash. If that is the case, if the pump kicks on during backwash, the pressure would rise. If the pressure continues to fall or stays the same, then the pump and plumbing before the pressure tank would be the limiting factor.
I measured the flow of the pump on its own at the pump house rather than at the well head and the rate was a fairly consistent 3.4 m3/hr. This would equate to 8.45 g/min/sq ft for my 1865 tank. Given the venturi system and katalox media etc adding flow resistance I guess that even if the Fleck valve adds some extra resistance the pump is definitely underpowered.
Downgrading your tank size would work but would likely require two tanks to get satisfactory results. Upgrading your pump is a better solution assuming your well can handle toe higher flow. How about an atmospheric storage tank? This can offer many benefits at a fairly cheap price.
An iron reduction system is generally sized when possible, to satisfy the usual consumption requirements, as long as the well, pump and plumbing can support the back wash requirements for that size filter. If you were to replace the pump, will the well support a higher flow and recovery rate to support a higher capacity pump?
Perhaps a cistern will be needed to hold a quantity of water from the well, so that a second pump then pumps water from the cistern to the home plumbing.
Alternatively, the current quantity of KL media could be split between two smaller size tanks with 1 additional control valve needed, thereby creating 2 separate systems plumbed in parallel. Each would then be back washed at different times.
Edited to add: Dittohead posted while I was keying my reply.
I reckon the well will support a much higher flow than I'd ever take. I've run the backwash for 2 hours a couple of times with no problem. Interestingly, though, when doing all the recent test I noticed that after 40 mins doing various tests one after another the lowest pump rate during backwash decreased to 5.4 g/min/sq ft! It was explained to me that this would be due to the well water level dropping thereby increasing the effort needed to pump the water up to the surface and therefore lowering the speed at which it could do so. I'll need to factor that in when I spec a new pump but I don't think I'll run out of water at normal usage.
A storage cistern's a possibility and I'll certainly consider this. Particluarly if I end up needing pH adjusting tanks and possibly a post aeration but pre pH adjustment filtration tank to ensure the pH reducing media does not clog up.
How much KL do you have in there?
When the pressure vessel/tank is empty and the pump starts during backwash, what does the pressure go to? Does the pressure drop below your cut-on pressure for the remainder of the backwash?
I've got 6 cu ft of Katalox in the tank.
Yes, once the pump starts it cannot run the backwash and fill up the pressure vessel and so runs continuously during the rest of the backwash and for a short time after the backwash has finished.
Once again thanks for all the replies!
Gerard