Big question . . . big answer.
Yes its K2O and P2O5, and the numbers indicate percentages of the gross weight.
It looks as though you know some chemistry, so try to put this in an Excel spreadsheet. Input a fixed qnty of the 4-15-35, displayed as N,P and K. then add a variable qnty of Ca-nitrate (also displayed as N,..,..,Ca) and see what you get.

Excel is very powerfull

The 5-15-35 are percentages of npk by weight.
You cannot combine 5-15-35 and 15.5-0-0 (cal. nitrate)and get 16-8-22.
Example: 10 lbs of each combined will result in each element added and devided by 2. 7.7-0-0 added to 2-7.5-17.5 = 9.7- 7.5-17.5. Less than 10 lbs of cal. nitrate means lower n and higher p and k. More than 10 lbs of cal nitrate increases n, but lowers p and k. Unless you add more P and k, you cannot change these ratios.

The problem is actually solved, but please read and confirm if I finally see clear:

But let's start all over again in a different approach, as my problem was misunderstood, probably because I didn't express myself clear enough. Actually I did mention to many options.

Assuming that all data and given percentages (of P and K) in 5-15-35 were actual content, it would be rather simple. But they are not. What the manufacturer gives us by 5-15-35 is actual Nitrogen content, but not actual P and K content in percentage. Both are given in conventional "fictional" P2O5 and K2O values. Hence, the actual P and K in PPM can only be calculated by using the formulas I gave earlier:

P2O5x 0.437=actual P
K2O x 0.83 = actual K

Hence, the actual content of the 5-15-35 base nutrient is like follows:

N=5 Nitrogen equals 5 actual N = 50 PPM
P=15 P2O5 equals 6.45 actual K = 64.5 PPM
K=35 K2O equals 29.05 actual K = 290.5 PPM

Using 1 gram/liter of our base 5-15-35 we got the following NPK-content in PPM:

N-50
P-64
K-290

One gram of Calcium Nitrate has a content of 156 PPM of Nitrogen and 185 PPM of Ca.

So by adding 1 gram of base fertilizer and 0.7 gramm of Calcium Nitrate (two different components), we've got 109 PPM N and 129 Ca which gives us the following formula:

N-159
P-64
K-290
Ca-129
________
Mg-30
S-40

The base is (+3) which means a plus of 30 PPM of Magnesium and approx. 40 PPM of Sulfur. (in case they give us actual Mg contntent) Which lives us then with a total PPM of 712 PPM which is fine so far. Problem solved? Well, actually not - because if I am going to imitate a commercial standard nutrient, I ain't still using the right maths. Because then again, I cannot compare actual percentage with industrial standard.

There still is a confusion. Reason: the commonly unknown- and uncommonly known fact, that in standard nutrient formula we do not deal with actual P and K content or percentage, but with a outdated industrial convention, that allows manufacturers to actually cheat on P and K content. Anecdotically speaking in this context, we cannot compare Apples with Pear sirup ;-)

Possible solution: weather we use actual PPM and hereby mean actual content, or we're use industrial standard NPK formula and mean "false" and not actual P and K content.

If we use PPM standard and hence actual content, we then must use data from nutrient formulas that are calculated in respect of actual P an K-content. If we want to keep using and comparing industrial NPK-standards, we must calculate using P2O5 and K2O standard, even if it is outdated and not considering the actual content. Btw: there is no such thing as P2O5 or K2O in any fertilizers, these are oxides which are toxic for plants and even not soluble in water ;-)

Am I right or wrong here?

I see your point. Since we're dealing with individual elements, why even bother with the industrial standard.
On this forum, when I see N-P-K values, I've always assumed the P & K were elemental not molecular. Interestingly (I just looked at a bottle), GH flora series listed P & K based on the industrial standard.
In response to your OP, I believe you would need to convert everything to elemental values to calculate the modified N-P-K. Then you would need to convert back to molecular if you wanted it listed in the industrial standard (to see speak to a soil farmer who doesn't understand chemistry, for instance)

Hi grizzman,

"On this forum, when I see N-P-K values, I've always assumed the P & K were elemental not molecular. Interestingly (I just looked at a bottle), GH flora series listed P & K based on the industrial standard."

I did not realize that "discrepancy" either, until I had to deal with this present problem of helping out that mate. And indeed most people confuse or rather mix-up both standards, as I did until now.

In case one is manufacturing his own concentrate (as I do) and calculating formulas according to the roles, it's always elemental. While people who buy commercial products (mostly) assume that the product specs. are actual NPK (elemental) values, while they are not. We think we are talking about the same specs, but in fact we aren't.

Perhaps this link might help. Or perhaps it might not. At any rate, check it out :)

Here is a link that might be useful: http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/opp2902#8

Hi shelbyguy,

Thanks, it might be indeed - although your link is about general information, while here I pointed out the confusion between two standards that get mixed up occasionally.

Let me put it in a simple equation:
When manufacturers and (obviously) users of commercial products talk about NPK-standard, they actually talk about the P and K values in K2O and P2O5. These are not actual P and K, though.

When people who mix their nutrients themselves (perhaps scientists) talk about NPK, they normally talk about actual P and K content, which can also be expressed in actual PPM.

Both standards are not identical and there is probably confusion in many cases. This becomes a real problem if someone recommends a specific NPK ratio, using elemental (actual) content of P and K, while the other person understands P and K as molecular (industry standard as in K2O and P2O5).

Example: Imagine there were inches and there were smaller inches too, and both were called inches! As long as you use "your" inches with a building plan in the same measurement standard, you do fine. But imagine getting to execute a building plan where they do use `your` inches for the main building and 'their' smaller inches for the measurements of the roof (or to picture it even better, the amount of stems instead of cut and planed wood planks). Will this roof fit with the rest of the house?