Ca to Mg
3tsp to 1tsp for a 90 gallon? Is that enough?

Ok, My question would be: If ratio doesn't matter--then why does it seem that many people with Hard Water (Gh 18), like me, wind up with Mg deficiency? I am assuming that the answer is in the 2nd part of the quote: That the Hard water is disproportionatly Ca and the Mg is used up creating a deficiency.......?

Right? Wrong?

TIA

I would like to know as well. My tap has 78 ppm Ca and 14 ppm Mg. If 5-10 ppm Mg is recommended then I shouldn't need to add any Mg then right? Mg deficiency is lighter leaf tissue and darker veins? Also my tapwater is high in Ca but why were the shells of my snails and shrimps never good looking? Is it because they need Ca supplemented in their diet?

You bumped a 14 year old post.

Ca/mg ratio is just a rough guess. All elements when too high will mess with the absorption of other elements. For example metals are usually toxic because they attach to the areas that Ca usually does.

Too much mg? I cant tell you what happens off hand but there is an element relationship chart out there somewhere.

When it comes to deficiencies or toxiticites, you will absolutely know when there is a problem. Your parameters seem fine.