Spectrapure CSPDI TDS Meter Question

So how exactly do you read this thing? It's the CSPDI 90 gallon one by the way. my out is at 0 and my in started at 250~ but is currently at 1.

 

I answered this in your thread on Nano Reef but here it is again:


The IN probe is RO only water after it has been through the membrane and the OUT probe is your RO/DI water. What you are seeing in the beginning is TDS creep inherent with all membranes, a simple DI bypass valve will help you there so that 250 does not exhauste your DI resin.



Neither probe tells you when to change the sediment and carbon block filters so you do that at 6 month intervals like clockwork. The problem with any dual inline meter is they only give you two TDS readings and you need a minimum of THREE TDS readings to troubleshoout your RO/Di system, tap water TDS, RO only TDS and RO/DI TDS. Without knowing your incoming tap water TDS you have no way of knowing of your RO membrane is efficient or not since you cannot calculate the rejection rate or removal efficiency.



I always recommend a good, inexpensive HANDHELD TDS meter rather than the inlines. HM Digital, the same manufacturer, makes a TDS-3, TDS-4TM and AP-1, all of whcih can be had for $25 or less and are much more accurate and versatile then an inline. It can test your tap water, your RO water, RO/DI, your ATO storage, the LFS water, your buddies water, bottled water, distilled water etc. The inline is dedicated to two spots and cannot be used portable since it requires flow past the probe inside the tee.



You cannot say what is good or normal on the IN probe since you have no idea what your incoming TDS is, if your tap water is around 250, the national average, then you might see 1-5 or so and be good, but of your tap is only 100 which again is very common and your IN probe reads 5 then you have problems.



The OUT probe should always read 0 after a minute or so of running time, when you first start seeing anything other than 0 on a consistent basis you need to change your DI cartridge and be looking at the RO rejection rate to make sure the membrane is functioning correctly. But to do this you need another TDS meter since you cannot test the tap without some replumbing of the meter temporarily to see what the tap water is.



Its easiest to get a handheld and toss the inline since you will soon find the handheld so much more accurate and reliable.