How much is acceptable TDS?

[CookieJar]

I've got a Typhoon III and it's worked great for me over the past year, however I've noticed the throughput is down 15-20% and the TDS has risen from 0 to 3-4. The slowed throughput doesn't bother me but what level of TDS is acceptable and at what level should I change the DI filter?

I plan on changing the sediment and carbon filters, but how frequently (i.e. how much is the allowable TDS level) to change the DI filter is what I wonder. At what TDS level do most people change the filter? I guess perfectionists will only settle for 0 TDS.

Thanks!

[dhnguyen]

That depends on what you keep in your tank IMO. If you're a serious SPS collector, nothing but 0 TDS will be sufficient.

I've used water with 3-4 TDS in my mixed tank without any noticeable drawback, however I do tend to use lots of macros for nutrient export so this may have helped to offset it somewhat.

I wouldn't go much more than 5 TDS though if you keep SPS.



D.

[J. Montgomery]

What is the TDS of your incoming water?

If your water has high TDS levels coming in, then you may not be able to get the levels down to zero in the first place . . . but if you normally get zero for months at a time (>6month), I'd replace the filters when your reading begin to increase (~2ppm). Decreased output flow is another indication that something is getting clogged up, and should probably be replaced.

[AZDesertRat]

Prefilters and carbons should be changed every 6 months like clockwork. Disinfect the filter housings at the same time. Prefilters and carbons have almost no effect on TDS, they are there for suspended solids not dissolved solids.
DI should be changed when you begin to see a consistent rise in TDS above 0. What perople forget is once DI resin has reached its capacity it releases contaminants back into the filtered water and in greater amounts that it was to begin with. I change resin when I see 1 to 2 on a regular basis.
You reduction in flow is probably due to colder winter water temperatures. Anything below 77 degrees reduces the flow. My 90 GPD Spectrapure unit makes 100 GPD in the middle of summer but is only doing 62 GPD at this time with the same pressure but lower temperature. To be sure it is not the membrane, test your tap water TDS, RO only TDS and RO/DI TDS to see how ell it is doing. You should be in the 96 to98% rejection range with RO only, if its below that you might need a membrane. Membranes should last 3 years or more IF you keep up with the required 6 month filter changes and disinfections.

[CookieJar]

Thanks guys!
I believe my incoming water is in the 160-180 range.
I'll change the filters and get on a changing program so the sediment and carbon filters are changed more frequently to maximize the life of the DI resin.

[Tunjee]

How do you disinfect them? Bleach rinse?

[J. Montgomery]

Originally posted by AZDesertRat
Prefilters and carbons should be changed every 6 months like clockwork.

DesertRat, I make ~10 gallon of RO/DI water per week, and when not in use I shut valves on all the input and output lines. My input water has 20-30 TDS. Do you still think I should be replacing the carbon filter every six months? I was hoping to get away with stretching it out further.

[AZDesertRat]

The prefilter and carbons protect the RO membrane. Using good quality filters and changing them regularly extends the life of the membrane which in turn extends the life of the DI resin and gives you better quality water. Periodic usage is probably worse than continous use as it allows contaminants to sit inside the the housings for extended periods. Once water hits the carbon chlorine residual is adsorbed and any bacteria or viruses present if they are still viable could potentially grow inside the housings, filters and the RO membrane itself. If you have never seen bacterial slime on a membrane its hard to imagine but its really disgusting. Changing filters and disinfecting the housings is one way to combat this, it forces you to check the condition of everything. Some less expensive carbons, especially granular carbon has a very small chlorine capacity, sometimes only a few hundred gallons worth and remember the waste flows go through the carbon too so figure 5 times what you have made for RO/DI has actually passed through the filters.
Use good quality filters and carbon blocks in the 1.0 down to 0.5 micron size and it has a greater capacity but it still needs to be serviced on a regular basis.
Disinfection is simple when changing filters. Remove the prefilter and carbon(s), disconnect the 1/4" line from the last carbon up to the membrane and stick it in a sink or bucket, put 2 or 3 tablespoons of regular unscented bleach in the first housing and reinstall all the empty housings. Run several gallons of water to flush it all through and reinstall the new filters and line to the membrane.

[CookieJar]

for disinfectant, how about just pouring boiling water into the removed cannisters into instead of bleach, that way you don't have to worry about residual bleach in your water?

[AZDesertRat]

Boiling water, unless you can keep it at a full lling boil for several minutes is not a substitute for disinfection. With a few spoonfuls and a good flush, residual in the housings is not an issue.

[Randy1]

My incoming water is 156 on my Hanna TDS meter. New Ro mem. was at 4 and new DI was at 0.

[AZDesertRat]

LUCKY. Mine is 835 incoming with 7 from the RO and 0 RO/DI. My RO works its tail off with water like that to get it to 7.

[CookieJar]

do you have 3 TDS meters in your system?
1 for incoming
1 for RO
1 for DI

Most places sell the dual inline TDS meter, which probably means you put 1 after your RO and 1 after your DI but none for your incoming (guess you can use a handheld one and measure that in your sink)?

[dhnguyen]

Originally posted by CookieJar
do you have 3 TDS meters in your system?
1 for incoming
1 for RO
1 for DI

Most places sell the dual inline TDS meter, which probably means you put 1 after your RO and 1 after your DI but none for your incoming (guess you can use a handheld one and measure that in your sink)?

um.. Why would you want to do that?

One handheld TDS meter should be able to test all 3 outputs IMO. A handheld TDS meter will be better for this.


D.

[AZDesertRat]

I have 2 dual inline TDS meters for a total of 4 monitoring points but I prefer my HM Digital COM-100 handheld TDS meter to them, its much more accurate. Inline meters are fine for an indicator but I always confirm readings with the handheld.
My inlines are after the carbon block or pre RO, after the RO or pre MaxCap DI (first stage of a two stage DI), post MaxCap DI and post SilicaBuster DI or final effluent. That way I can monitor what is going into and out of the RO membrane and what is coming out of each seperate DI so I know when to change DI cartridges. It kind of elaborate but very effective. I also use two pressure gauges, one on the incoming line and one after the carbon block or pre RO membrane so I can judge the condition of my prefilter and carbon block to prevent pressure drop from fouling or sediment plugging. Next I am adding a flow meter so I can tell exactly how much water has passed through my system to judge filter lifespans. I am a little weird I suppose but water treatment has been my profession for 33 years and things like this intrigue me. I know I need to get a life!

[CookieJar]

Des.Rat- Damn, that's hardcore!
1 microscopic TDS doesn't have a snowballs' chance in hell of getting through your system.

[Tunjee]

I've seen bacterial slime. I work on ice machines sometimes. OH and the colors are interesting too. Condesnsate pans are the best though. Bacterial sludge! So bleach sounds like the easiest and most effective way to dissinfect. I"ll give it a shot next time I change filters. Thanks.