[borg]

Hi i have a 300gpd RO DI unit and my ppm has just started to rise since last week it is now at 6ppm when changing the filters do you have to change them all. i have never changed them before i have had my WFP for 8 months and this all new to me so i hope some 1 can help me cheers.

[Paul Coleman]

Hi i have a 300gpd RO DI unit and my ppm has just started to rise since last week it is now at 6ppm when changing the filters do you have to change them all. i have never changed them before i have had my WFP for 8 months and it is new to so i hope some 1 can help me cheers.

If you haven't changed the pre-filters, do so now.  If you are lucky, the membranes may still be OK.  I think the general rule is to change 20" pre filters six monthly or if you have 10" pre filters, change them quarterly.  Membranes should only need changing every two or maybe three years (possibly longer in some systems).
If you have a sealed DI resin container in the final housing before the tank, a refillable one may help you.  I switched to a refillable one and it gives me more control of how pure the water is when it enters the tank.

[borg]

i do have a sealed DI resin container so do i change all the filters and resin then sorry about this as i say this is all new to me.

[Paul Coleman]

i do have a sealed DI resin container so do i change all the filters and resin then sorry about this as i say this is all new to me.

Well you should certainly change the pre-filters as a matter of urgency if you have been using them for 8 months because not doing so could mean that you have to change the membranes.  The chemicals removed by the pre filters (there is a carbon filter asd a sediment filter usually) can wreck membranes that will normally have a lot more life in them.
I didn't trouble myself about the DI resin container as I also had a resin vessel in the van so I could polish the water off as I used it anyway.  However, I decided that I wanted pure water in the static tank instead so got a refillable one.  The refillable one goes into the same housing as the sealed one so it's not a big deal switching.
I am hoping that the recent climb in TDS is about the resin starting to expire rather than any pre-filter/membrane problems.  A pre-filter/membrane problem is normally accompanied by a rapid rise in TDS and a dramatic drop in pure water production so it sounds like you may have got away with it - just.
If you have a DI polisher in the van then a sealed DI attached to the RO should be OK.  If not then I suggest a refillable so that you can keep the TDS at 000 more easily without regular changes of the sealed unit.  A lot of it is a matter of personal preference.  Changing the pre-filters isn't though.  If they've lasted 8 months, I assume you have the 20" variety rather than the 10"?