TDS levels on DI filter?

So trying the search, but somehow seeing nothing for the terms “DI”, “filter”, “TDS”…maybe since I’m not active over on this side I’m limited on results, IDK… Pretty simple question for the DI filter guys, at what TDS level do you swap out a filter?

I use the Unger Hydro Power and usually change out the bag at around 18-25. I have however run it up to 38 once or twice with no discernible issues.

This is starting with TDS of 188 to 225 in St. Petersburg, Florida. I had one property a few years ago with 450 TDS! and changed filters before finishing the job. Don’t know what was in that crap.

As I understand it, it does matter what is in your water that you are having to filtering out.



Around 20-ish we swish the resin around and get some more life out of it.

When it hits 20-ish again we start keeping a close eye because its going to go up FAST at that point

Don’t automatically assume that because the resin is bad hen it starts pushing out anything but 000. Sometimes the water from the spigot is really high and the resin can’t knock every last bit of it out.

welcome to our world in California with 450-500 TDS all the time

and if the DI discharge hose gets kinked, bam, DI cartridge bad in no time


It depends on the job. If it’s a very high paying tall job then I make sure that it’s 003 ppm or less. If it’s a regular job, not too high then it’s 010 or less. I like to see what I’m getting as a result if I let it go higher.

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All our jobs pay roughly the same per window…I’m having a standard that keeps from having spotted windows on all jobs, that’s the number I’m looking to establish.

Just keep it under 20 and you should be fine. When it gets over 10 I’m testing it on every job to be sure

Our guys test in in-house in thhe morning when they have a window cleaning on any of their jobs,but they’ve been telling me they have been swapping out the resin tube when it gets higher than 4. I feel like that’s maybe overkill, and I’ve seen us obviously going through way more resin than we were last year…hence the reason for my polling everyone :wink:

with 450 tds going in, RO puts out 30-40ppm, i have forgotten to check Di levels before starting and its been at the RO level at the brush like maybe all day a few times and it all looks fine, makes we wonder why im messing with DI resin to begin with these type of great results, but then I would find out why at the most inopportune time and I dont want to do a job again, so I keep up with the Di cartridges lol

any input on this? a DI only system, once it hits 10 shoots to spigot TDS in a very short time and white spots everywhere start at 10-15TDS, but RO only out at 40 TDS looks great, crazy


RO and DI probably filter out slightly different material.

We have several ro/di units. Some with a 10” di housings and some with 20”. The 20” di can knock down more ppm. When Incoming tds is really high, outgoing tds can be 5-10, but then the next job, it’s back down to 0 because the incoming tds is lower. The systems can only filter so much.

A VERY unknown fact is that RO membranes are more efficient when you have a pump raising the pressure before the membrane. If our ro/di system is unable to handle the incoming tds, we slap a pump before the system and then it’s fine. We pretty much use pumps for everyday use now. Instead of the RO knocking the tds down to 30-40, it knocks it down to almost not needing the DI. Saves us lots on DI costs now.

We bought a bunch of the Tucker booster pumps. I know there are probably cheaper options, but we really like how solidly they are built and love the adjustability

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