Cal/Mag is critical to healthy plants and typically isn't contained with other nutes in large amounts due to the chems mixing, binding, and then precipitating out of the solution where it is unavailable to the plants. If your water has high levels of calcium then that is ok. most often in soil cal/mag is usually enough, plus most people use dolomite lime in soil which has both elements. But in hydro, you cant use lime well as there is nothing to break it down, so the additive form is necessary.
Many of the nute companies want to sell nutes so they "assume that you know all of these little tricks", so they don't tell you everything, such as the need for certain additives that cant be included with a one size fits all nute. That is why I prefer a 3part nute because it is able to keep the important nutes separate that need to be separate but still have everything that is needed for the nute base.
These 3 part nutes can carry a grow from start to finish without any additives, buuut by adding some stuff, you can "punch-up" the grow some depending on the additives and the needs of a particular strain. It is next to impossible to know just from study which brands will have all that you need without them blowing at least a little smoke at ya. That is why its best to talk to others to see what they have had success with, and what the differences are for the pros and cons. All nute brands have their pros and cons because there is no one brand that is "perfect for growing". This is because MJ comes in so many varieties that have different needs, and then there are almost endless grow situations that affect how well a particular nute will do, and what extra stuff may be needed.
I love Jungle Juice in coco, but it requires extra calmag and constant monitoring and adjustment of pH. That is because it doesn't include pH buffers in its solutions. I however, prefer to have a fairly wide pH swing as I have found for my grows that it makes the plants quite healthy.
Many people here love the GH flora 3part as it is very similar to JJ but has buffers that help balance the pH a good bit. I haven't used it so I cant give pros or cons on it. It does require the calmag additive when used in hydro as this is typical of hydro as opposed to the nutes as most nutes do not hold enough calmag in solution for hydro for the reason I stated at the beginning.
If you go to the Advanced Nutrients site, you will see that they offer a slew of additives and nute varieties, and they will let you spend lots of money on these additives while knowing that if you use JJ 3part, you don't need all of them. But at the same time Most of these companies do the same.
If you ever have tropical fish and buy fish food, you will see that the manufacturers advise feeding fish 2-3x a day as much as they will devour in 2 minutes. If you go by that, your fish will be dead in a week and your tank will be filthy. Fish don't need to be fed but 2x a week (not 2x a day). But the fish food companies are trying to sell food and they figure that if you know what you are doing then you will not even look at the directions.
So which nute brand is best for you? If you don't have a lot of growing experience, then I would say GH flora 3part. More experienced growers will experiment with other brands to see about optimizing their grows but for new growers GH Flora will be the best bet I think. Or Jungle Juice 3part If you are more of a hands on type of person
