I've always had IO at about 340-350 or so. Mg is low too, usually around 960-1100

Reason for the post was basically to point out water changes alone made with IO won't be enough to keep the Calcium up.

Doug, what this amount by Ben bit?

Read this thread of Bens (Littlesilvermax) Link

. I am also using his chemicals and dosing my RO/DI water with MG and Ca then adding my IO salt. It took a little testing to get the amounts perfect but now every time I mix up a batch of water I can dose the same amount of Mg + Ca to have my water come out at Mg 1300 and Ca 400. Works really well.
I used the reef calculator to get my amounts close then adjusted accordingly after testing Reef Calculator
Can't beat the price either !!

Are you using magnesium chloride or sulfate(epsom salt)? And how fast does the mg drop in your tank?

According to Littlesilvermax, Food grade magnesium chloride mixed with a small amount of magnesium sulfate (I used Randys Recipe in the Calculator to get my mg in the ballpark).

By dosing my weekly water change water to desired levels my Mg has stayed at 1300 (Elos ) since I got it up to that. I have to add about 1.5 Tsp / week of Ca to keep Ca at 400 (I used Dow's Flake in the Calculator).

Thanks. I was looking for it.

Mine seems to stay around 1350ppm at the present time and my calcium around 420ppm with just kalk additions and a 5gpw water change.

Hey Doug, are you having to do any additional Ca dosing (besides your reg water changes) to get your Ca to stay at 420? Like I mentioned above, I'm having to add about 1.5 Tsp / weekk to maintain mine. I'm only doing about a 7% water change once a week in my 60 g system. But it is really easy, I like this system

I drip kalk, but not every night. Most of my corals are still frag sized, so not a great demand from them. I assume my clams, esp. the Derasa,s which are growing like weeds and the heavy coralline on the rock are consuming a fair bit.

So besides dripping kalk on occassion, just the water changes for now, seem to be doing the job.

new bucket, new numbers
 

Started another pail of IO and low numbers with this one as well.

Made up 20g ro/di then left for a day with a couple of small pumps to aerate, added 12 cups of IO and then left mixing for another day.

Tested today and have:
SG: 1.025 refractometer
Ca: 270 Salifert and 300 twice with ELOS at 71°, thought maybe sample temp so warmed to 78° and got 275 ELOS.
Mg: 900 ELOS
Alk:10.9dKH Salifert
pH: 7.8 using pH monitor and after replacing battery and recalibrating probe.

Either I'm doing something wrong or IO is.

IO has always mixed that way for me for the last 8 years. Ca always low 300's, alk around 10 -11.