Low magnesium

I just got my magnesium test kit, and I think this may be some of my problems.  Here are all my parameters:

Yes, maybe I should just do some water changes.  If I add that much epsom salt I will also add a lot of sulfate.  I looked at petsmart (the local fish store), and they don't have anything to add magnesium.

Don't worry.
It would take a year of adding Epsom Salt with no water changes to cause any problems. You have adequate biofiltration which includes the sulfur cycle to handle the Epsom Salt.
Water changes won't get you close to the amount of Mg needed, unless you plan to do a 90% change.
Don't let common new hobbyist paranoia get the best of you.

I use a combination of epsom salt and a magnesium cloride ice melt disolved in RO to raise my levels.

Slow is best. Mark would know how fast you can increase it daily. I use 'safe step' brand. it's called, I believe, 'extreem 8500'

I use instant ocean salt, although I do very few water changes.  My goal is to figure out how to maintain water quality without water changes (or at least very few).

Do not add in all 3 3/4 cups all at once that needs to be done over a week or two...also instant ocean is not high in cal,alk,mag,strontium so waterchanges with instant ocean will not help your levels too much.... for an alk/cal supplement I use kalkwasser(aka pickling lime,aka calcium hydroxide) and I love it... I just use kalk in with all my top off water.

Cal/alk/mag are your 3 major elements in your water that you need to make sure are pretty stable(stable being more important then precise numbers)... so to me I would not just add in epsom salt or known as magnesium sulfate... sulfate is sulfur.. chloride is always the better "transporter" of anything cal/mag/strontium etc etc etc... so to get a "perfect balance" you need to use both mag chloride(in a lot higher of quantity then mag sulfate) and mag sulfate.

The calculator says not to increase the magnesium by more than 100 ppm per day, which comes to about 3/4 cup per day of epsom salt.  If I could find some magnesium chloride locally I would use it.  I will look again next time I am at lowes, home depot, or walmart.

Edited by Davidwillis - January 08 2011 at 11:14am

I did some more testing today, and I am not sure I am using my test kit correctly.  I am using the red sea magnesium kit.  After adding the A, and the B, you add the C until it changes from pink to blue (there is a color chart).  When I get to about 850 it changes from pink to a blue/purple (but not as blue as the chart).  After adding a few more drops it stays that color, so I thought that must be it.  But today I tried adding more, and it went back to pink, then back to blue/purple (bluer than the first time, but it never gets all the way to the blue on the chart).  The second change happens at about 1300,  It may get slightly darker after adding more, but it never gets to the blue on the chart.