Would you? TDS question

[Michael43]

I have the traditional handheld TDS/temp meter. I made ro water with my BRS 150gpd unit like usual but this time with the booster pump for the first time because I had low pressure(40psi). This time it made the psi like 90. I made the water fast. The TDS meter on the ro/di said 0. My handheld meter says 2-3. It always used to read 0-1 with the low pressure. I realize and have turned the booster down to about 70(lowest it will go) and will change out some carbon blocks next time. I'm sure I'll be back to my 0-1. My long winded question is that I have the salt mixed and running at temp for a change tomorrow AM. I have sps. Would you dump it or use it? Again it was only about let's call it 3 TDS on the handheld but still read 0 on the digital meter

 

[AZDesertRat]

Inline TDS meters lack the accuracy of an ATC handheld. Trust the handheld and forget you own the inline.
Turning the booster down is counterproductive, RO membranes get more efficient at higher pressures and the rejection rate goes up, not down.
With a TDS of 2-3 I would use it but you need to do some troubleshooting to see what needs replacement. At minimum you need new resin but you need to use the handheld and see how your RO only TDS is doing.
The other thing is dual membranes ARE NOT water savers no matter what some misinformed or less knowledgable vendors try to tell you. Unless you have softened water and lower than normal TDS your waste ratio needs to remain at 3:1 to 4:1 so you don't kill the membranes. Think about it, you are sending the brine or concentrated waste from one membrane into the next then reducing the waste even further, membranes must be flushed when in use, there is no getting around it. If it were really that easy vendors with multiple decades of research and develpment would have been doing so 25-30 years ago. Everyone is looking for a better mousetrap but simply cutting the waste is not the way to go about it.

 

[Michael43]

Ok i will change the water with this. I was trusting and going by BRS on this one. They told me to get the pressure to 65 psi and that's where the system will be optimized. I do use a water softener in my home but my taps TDS from a well is very high. I, just before this time making water changed both di resins and the first "foam" filter was changed not long ago. Just the carbon blocks are still original and I ordered 2 more to change them out.

 

[AZDesertRat]

Are you using bulk resin? If it was previously opened was it resealed with a seal a meal type vacuum sealer and stored in the refrigerator so it stays damp and fresh? This is important. Resin has a short shelf life even when unopened and properly stored and once it is opened it starts to dry out and lose its anion and cation electrical properties. I tried bulk resin and gave up on it in favor of better resin in prepacked cartridges that lasts me about 6 times longer than any other resin I tried previously. Bulk ended up costing much more due to frequent replacements.

65 psi is the bare minimum pressure it takes to operate a dual membrane system, 80-100 is much more efficient. I have run a single 75 GPD membrane on an Aquatec 8800 booster set at 95-100 psi for over 8 years now and still getting 99.4% removal efficiency at 135+ GPD on 560 TDS softened tap water with the original membrane still in place. I get over 1000 gallons out of a single 20 oz MaxCap DI and 3000 gallons out of a single SilicaBuster DI compared to the 150- gallons I got using bulk resins from every source I tried.

 

[Bdog4u2]

Have you calibrated your hand held lately i have a Milwaukee tds and it needs it a few times a year

 

[AZDesertRat]

I check calibration occasionally but I find it to stay pretty true as long as I rinse the meter in RO/DI or distilled water after each use and make sure it is capped when I put it away.

 

[ReeferBob]

I change my DI when TDI gets to around 10-20. I don't worry about TDS below that amount. Mine starts at 250. People used tap water for years with no issues - a little TDS is not the end of the world.

 

[AZDesertRat]

Not a good idea.
The problem is DI resin starts releasing weakly ionized substances even before it is exhausted and since these are weakly ionized they don't show up well on a hobbyist grade TDS meter. It gets released in big spurts since it has been accumulating on the resin beads for 10's or 100's of gallons. Some of these include phosphates, silicates and nitrates among others which are not good for the reef.
Since you have absolutely no idea what that 10-20 TDS is and the fact it is very likely higher than what you are able to measure I would discourage this practice. When you first start seeing signs of anything other than 0 TDS on a consistent basis it is time for new DI.
I also used tap water for the first 15 years in the hobby but it was nowhere near as troublefree as the last 20 years have been since switching to RO and finally RO/DI about 15 years ago. No comparison.