You need a TDS
meter to check the water and that will tell you when you need to change out the resin. 0 is waht we want on a TDS
reading, I run my filters up to 16-19 on the TDS
. As long as I have 0 PO4
I keep using the filters. Some guys change it out as soon as it starts going up.
AWI has some good resin and so does resindepot, I have used them both.
the color is a orange when its used up. But get none color change and a TDS
meter. The non color change is usually cheaper.
I picked up the in-line TDS
meter from AWI and I love it..