I assume your talking about a
TDS meter (total disolved solids). It measures how clean the water is.
What to do with it.
1) check your tap water and record level
2) check water comming out of membrane before the DI and record level
3) check your final output water and record level.
Depending on what reading 1 says, how high your pressure is, and how big the unit is will determine what percent cleaner the membrane water (reading 2) is compared to your tap water (reading 1). But in practical terms the membrane should remove about 80 - 90 % of TDS. (you'll never get what the membrane is spec'ed for except under the best conditions)
Example 1: reading 1 says 100. Reading 2 says 15
membrane removed 85% of total disolved solids.
Now check reading 3. Most reefers want it going no higher than 5 or 10 at the most but never within 3 or 4 of what reading 2 says. When reading 3 approaches the 5-10 or within 3 or 4 then it is time to change the DI cartridge.
Example 2: if reading 2 says 11 you would not want reading 3 to ever go higher than 7 or 8
When membrane reaches about 70% of removing the TDS's then it is time to change the membrane. see example 1
You should change your pre-filter and carbon at least every 6 months. If your on city water (with clorine) or a shallow well (depth of well less than 150') and reading 1 is really high you would want to change it sooner than that.
It's a little hard to explain in writing but hope this helps guide you on how to use the conductivity meter and when your cartidges/membrane needs replaceing. If reading 1 is really high then you would want to get a second add-on DI cartridge (it would save you money in the long run). If you go that route the method for determining when to change the two different DI's is a little different --- let me know and I could explain that.
Charles
