So I've been struggling over a couple questions I have about what are some proper levels for different nutrient specifically Ca and Mg.

I've been reading that levels of Ca in a planted tank should be around 30ppm. Is this correct? I've also read that a GH of around 100ppm is ideal. Wouldn't this mean ideal Ca levels would be around 75ppm and for Mg 25ppm???? I know the ratio between the two is suppose to be in the 3:1 to 4:1 area. At least on that almost everyone agrees. I'm just so confused at this point on the right ppm. The more I read the more conflicting ideas there are for the right levels?!!?

Please share what your opinion or the right answer is, if there is one!! Or what has worked for different people. Specifically in high light tanks with CO2 injection.

Help!

the correct answer is.. what do ur plants need? if ur plants use all the available calcium before ur water change, then u need more!! if they don't then u don't need more

While it may seem a way to avoid the answer, the above is true. Too many times we read and read and then finally find out that there is no one true answer. Since all our tanks are different, with different fish, plants and even water. There is no one true way for us to operate. The amount and type of food will differ, the fish and plants will differ. So it is quite logical that the answer for how much CA and MG needed will also differ. Many folks like to promote a specific answer but that is really just not telling the whole story.

You might be able to go to a lot of study and find what one of your plants likes best but then likely the plant next to it might like something different. Most of us settle for a "ballpark" figure and try to let the plants tell us if it suits them. Many times in my tanks, if a plant doesn't like what suits the group, they have to die!

Awesome great answers. So what I'm taking from this is that ratio is the most important thing? So an additional question if that is the case. My water is super soft. I typically add caco3 to bring up my calcium and kh at the same time. Is there a point where ca would start interfering with uptake of normal levels of other nutrients?

Getting into a really grey area for me. More things I learn the less I understand!! I'm sure there is a point where it becomes bad. What that point is, will likely vary and I don't have a good answer for where that point might be.

I should have paid more attention when in school? Or is it that I've forgotten all those things I never planned to use?

It is important to have some calcium and some magnesium, enough of both that it meets the plant's needs. Unless someone has some data to show what the "best" levels are, I don't think it matters what our opinions are. Also, to the best of my knowledge, it doesn't matter what the ratio is, just that there is enough of each. If there isn't enough, then adding some more should give you noticeable changes in the plants. So, if you want to try to figure out what is best with your tank and plants, just add some of one of them, calcium for example, then watch the plants for a week or so to see if you can pick up any improvements. If you can, add a bit more, and repeat until you don't see an improvement. That will be the "best" level. Then repeat with magnesium. You could probably start with magnesium and get the same results. I'm betting you may see some effect of adding some more magnesium, but probably won't from adding some calcium.

Then, there is manganese. I understand that it has value too, and may be in short supply. So, you could do the same testing with manganese.

http://www.fao.org/docrep/003/X6862E/X6862E03.htm

maybe this will help

I'd just use a standard GH booster, no need to add KH.

Liebig's law of the minimum applies strongly here.
Sort of like the Law of Gravity in physics, you are not going to get around it or avoid it.
http://en.wikipedia.org/wiki/Liebig%...of_the_minimum

Another view:

http://en.wikipedia.org/wiki/Rate_determining_step

A 3rd way/analogy:

http://en.wikipedia.org/wiki/Theory_of_Constraints

These are saying pretty much the same thing, thus the ratios matter not, the weakest link, the most limiting resource, the rate limiting steps do.

These determine the rates of growth in plants, there are no special exceptions to this rule. This rule also can have resources like CO2 ppm, light(Intensity, color spectra, duration etc), current.

I've run some very low GH's for Ca and Mg. I've also had tap waters with very high GH's for both Ca and Mg as well.
Basically 2ppm up to 200 ppm for Ca++
0 ppm up to 52ppm for Mg.

Yet to hear of anyone that's tested over this range in a planted tank. Most every issue I had was related to high KH, not GH.

This is easy to test if you have low KH tap water by adding the GH back and not altering KH.

This may not be you , so please don't take offense. I mean it as a general statement.
We sometimes get too involved in one small item that we notice and forget that it is not a big part of the overall question.

In my case, I have very hard alkaline water. Probably not the best for raising plants. But from my rookie position, I don't worry about that. It would be like sweating over bugs on the windshield of a car that won't start! If/when I get a better handle on the big items, like lights, CO2 and macros, I may get around to worries about the CA/MG. For now, I know I have plenty. It shows up on the glass every time I splash water.

having a hard water doesn't always mean you have enough Mg, it might be 100% Ca only and 0 Mg, i had this coming out of my tap water where there is plenty of Ca and no Mg at all.

This is very often the case. Most assume that high GH means plenty of both, but........this often gets folks into serious growth issues. I had this a long time ago.

I personally have water that has 30 ppm CA and 0ppm Mg. The KH of my water is about 2.5dKH so I need to bring it up to prevent my water being super low in pH when I get get the right level of CO2 (I used the high tech method of injection). I add enough Mg to reach that 4:1 ratio since over the course of the week it ends at 3:1 with Ca being used. Although, now it sounds like that ratio isn't super important either.

Previously I noticed when I used baking soda to bump the KH to an area that worked by the end of the week my plants would stall because they used all the Ca!!! So that is when I started using CaCO3 to increase both. Not to mention less sodium in the water. I've just have had some deficiencies in micros, iron, and phosphate lately that I hadn't previously and I didn't know if it had to do with my calcium being up between 65 and 75 ppm now. It doesn't sound like at that level it really would matter significantly from what you all have said. So maybe it's just the limiting factors now like that law states? So I should up my levels? Does that sound right?

ratio, 4:1, 10:1, 20:1, 60:1,60:10 etc will work, same for 10:10, 10:5, 30:10 etc work too, but plant don't use much Mg, they use more Ca, 30ppm of Ca is plenty for high light tank, 8ppm or less Mg is also good enough

i had set a test where Ca and Mg was dosed only at 0.10-0.20ppm daily, plant still grew but lost their colors, they will make you think that you are not dosing enough Fe, but that was not the case, simply adding more Ca and Mg corrected the problem.

if you ask me and i have to estimate the total amount they use on the high tech everyday then it would be around 0.50ppm Ca, 0.20-0.30ppm Mg, this is based on what i think, you don't have to agree with it.

Awesome, well my mind is at peace about GH and acceptable levels. Seems like I'm over thinking things. Thanks everyone for the helpful posts!!!