Stages in an RO/DI unit

[dingo0722]

So I changed the filter in my RO/DI filter and I used a 5 micron, a 1 micron carbon and a 1 micron before the RO unit. The filters were made by Kent. After doing this My tank had a massive outbreak in cyano. Since I have not had this problem before I was not prepared to test for phosphates. I ordered a test kit along with a phosphate sponge and a TDS meter. Does anyone know what stage in a RO filter do phosphates get removed?
Also are all the filters in RO units interchangeable? I have a standard 10" clear canisters
Wondering if I should junk the entire unit and buy a new one or if I just need the correct filter stages

 

[scsinet]

Yes, the filters are interchangeable.
Phosphates are usually removed in the final (DI stage), but I don't see one mentioned above. Usually you have things laid out like so:
(1)Sediment Prefilter >>> (2 Optional)Second Prefilter stage, usually 1 Micron >>> (3)Carbon >>> (4)RO Membrane >>> (5)Deionization
Are you missing that last stage?