You cant test salt water with a TDS.. the numbers would be through the roof
TDS Reading
in Forum > Questions & Answers
Hi,
I just received my TDS meter :) (At Last)
I took some reading just for fun:
RO from the store = 5 ppm
Tap water = 100 ppm
I would like to check how my tank is but I don't know how much TDS is good in the tank. Any idea?
yea, the TDS only works before you add the salt. it tests the "total disolved solids", and salt is a solid so it doesn't work with salt. the tds meter is made so you know how much tds is in your water BEFORE you put it in your tank...you need to know this with top off water, AND water that you are going to mix for water changes. 100 tds isn't bad for tap water, actually...BUT you don't want to EVER use anything higher than 10ppm...i never put in anything more than 4ppm...the closer to 0ppm, the better. i think i had told you before that the RO at the store is usually pretty high compared to what you REALLY should have (especially with amemones) because they don't filter their water for reef tanks...they filter it for people...and we can handle the TDS (even though it probably gives us all types of problems down the line)...and always go with the frame of mind that ANY TDS meter is PROBABLY reading about 1ppm lower than what the water ACTUALLY is...they aren't 100% accurate. RO unit time miss! 
