what should TDS levels be at ?

i hook-ed up a ro/di and today a tds meter to know when to cheange the filters but cant find any info on when it time..at present the water going in is at 345 and coming out at 0.. im assuming it will eventually start coming out higher than 0 but when is it time to change ? or anything over 0 means time for replacement? ty

 

AZDesert is the most qualified to answer that question. I know that 0 TDS is good and if it gets above 10 I think, its time to change cartridges.

 

If you are able to get zero now, then consider changing once you get more than zero. The first thing you will likely need to change is the DI resin. I like the color-changing DI resins that show you when they are used up....but the best indication that they are used up is a rising TDS.

Prefilters should be changed every 4-6 months.

RO membranes every 1-2 years, depending on volume and membrane types (although flushing the membrane periodically increases lifespan).

 

Change at a TDS of 1.

 

Your inline TDS meter should be hooked up so the IN probe is after the RO membrane and the OUT probe is after the DI filter. The tap water TDS is not as important as those other two and can be obtained any time by swapping a few fittings. Its the RO and RO/DI you need to monitor.

You change the RO membrane when it is no longer economically feasable to keep changing DI resin. A new membrane should give you 96-98% rejection or removal efficiency so with your tap water TDS at 345, once you correct the IN probe you should expect to see a RO only TDS of say 5 to 10 maximum.

You change the DI resin when it consitently shows anything other than 0 TDS. The better the RO TDS is the longer you will be able to maintain 0 TDS from the DI. Color changing resins can be very inaccurate and most turn colors too late and you are already passing TDS, always use a TDS meter.

Prefilters and carbon blocks have very little to absolutely no effect on TDS, they are there to trap suspended solids, big stuff, not dissolved solids or TDS which is the job of the membrane and DI resins. You shouldchange the prefilter and carbon at 6 month intervals like clockwork regardless of how much water you have made. Remember even the wast goes through them so you have processed 5 times as much water as the RO and DI have seen. They protect the expensive RO membrane so need to be kept up with and should always be quality filters, not ebay quality.

RO membrane last anywhere from 18 months if you use low quality prefilters and carbons or do not replace them as recommended, up to as long as 10 years by using high quality replacements. Contrary to popular belief, flush kits have no proven benefits, they give you a warm fuzzy feeling is all. Keep the waste ratio at 4:1 and the membrane gets all the flushing it needs every time you make water, don't waste money on a flush kit if you don't already have one.

 

great info thanx..BRS so not ebay specail,,lol

 

Good unit, just use the 1 micron or smaller replacement filters when the time comes (6 months) and it should last for years.

 

I have a ZeroWater filter and it says to change the filter when you start getting a reading of 6 TDS. Nobody can give you a timeframe on when you will have to change your filter because some have double the TDS of others in their tap. For example, my tap is cleaner than the national average (~250) at around 170 TDS.

 

TDS coming out of an RODI should always be zero. If it's not, you need to replace your DI resin.

Zerowater is a DI-only system, which is going to give you water as pure as an RODI, but DI only makes it burn through resins super fast compared to RODI. You should also replace at 1+ TDS for tank use.

 

Just as tap water TDS varies so do things like CO2 in the water which also affects DI resin life. The national average TDS is close to 250 so you are slightly lower than average.
IO would not wait until a TDS of 6 though. Whomever sells those units os probably not a reefer themselves and may not understand the needs of a reef system.
What you need to know is DI resin starts to release weakly ionized substances even before it is exhausted. A few of those substances are nitrates, silicates and phosphates, all of which can be bad at any level at all. Also weakly ionized substances may not register well on a hobbyist grade TDS meter so you may not even see a reading and can still be sending bad things to your reef.
By changing the resin as soon as you start to see anything other than 0 TDS you reduce those odds.

I use a rule of thumb of betwen 3000 and 6000 total TDS per pound or 16 oz of DI resin. If you have CO2 lean towards the 3000 number and if your water is pretty good its closer to the 6000.
So say your RO only TDS is coming out at 10, you would get somewhere between 300 and 600 gallons per pound of resin. The average full size 10" vertical refillable DI cartridge holds 20 oz of resin when packed properly so add another 25% to those numbers for a fresh full size refill.

If as Blackraven says your unit is DI only then you are sending 1 TDS of 170 directly to your resin then you can expect maybe 18 to 36 gallons of 0-1 TDS water from 16 oz of fresh resin. (3000 divided by 170 or 6000 divided by 170). Not knowing how much it holds you would have to adjust your numbers accordingly. Does not look promising to me at all though and will kill you in resin recharges or replacements.