Problem: Recurring algae – Pressure in filter jumping from 17 PSI to 35 in 1-2 hours

Background:
I purchased a home with a pool about a year ago and have been battling black algae since day 1. This has been managed for the past year effectively enough through blood, sweat and tears. It is a 60x10 lap pool using an FNSP60 DE filter. I have a number of mesquite trees nearby and have quite a bit of organic matter to deal with on a daily basis. I normally had to backwash about every 2 months (last year swim season).

Last month I got back from a business trip (5 days) and the pool had turned green. We have not been able to get it stable since that time. I am consistently dealing with high pressure in the filter with little to no water movement and new green algae growth. I have a company managing the chemicals on a weekly basis (which turned into twice weekly the last 2 weeks). They are putting 4 times the normally required chlorine for a pool of that size including conditioner and it is not “taking”. Zero FC after 2-3 days. I have a side suction pool Shark and brush daily for the black algae. I have taken the filter apart and cleaned thoroughly after backwashing. I have also spot cleaned the grids with the lid off twice during the last month after backwashing. Still no positive results.

I introduced Algaecide for the first time 2 days ago (against the recommendations of the pool chemical company) with initial positive results. I can now see the bottom of the pool and most of the top layer algae has either gone into the filter or dropped to the bottom of the pool. I backwashed again (adding more DE) only to have the pressure spike to 35 PSI after 2 hours. I am going through D.E. like crazy due to how often I am backwashing and cleaning the grids while making very little progress. I’m hoping to find a better management strategy to get this under control. Is there anything I am missing that could be causing the pressure to sky rocket so shortly after a backwash with fresh DE? I normally add 7 lbs.

Possible issues and next steps I am thinking about:
- Replace D.E. filter grids
o I am NOT seeing DE in the pool and do not believe I have a hole in the grids but the plastic “skeleton” on many of the grids are damaged and broken in part.
- Filter Grids placement in filter
o The grids are sandwiched very closely together against the vertical pipe. I am concerned there should be more room and this has contributed to the damaged “skeleton” of the grid as described above.

I’m hoping someone who has gone through similar issues will have some insights on a better/different strategy I could be using on the pool maintenance.