I have a 3 stage IPC Eagle system. I’ve had it for about a year. Only clean windows part time and probably went several months without using it. Cleaned a house today and TDS read 6. What filter do I need to replace?

You would need to replace the pre-filters and the DI cartridge. If you have the Hydro Cart, you would want to order this kit. https://windowcleaner.com/ipc-eagle-carbon-sediment-di-filter-set-for-hydro-cart