Because my water doest have enough for guppy fish its recommended to have 100-150 Mg/l I get 40ppm
There is more to this. First, there are three inter-connected aspects, GH (the general hardness which is basically dissolved calcium and magnesium in the water), the KH (carbonate hardness or Alkalinity), and pH. Generally, the higher the GH, the higher the KH and pH. Not always, but these do generally go together.
Fish are most affected by the GH, then pH. So with fish requiring moderately hard or harder water, such as guppies, the main consideration is the GH of the source water. The KH really doesn't matter, as the pH will tend to be basic (above 7) which such fish also need if the GH is on the hard side. And with a moderately hard GH, the KH will be comparable.
The same works in reverse. Soft water fish tend to also prefer acidic pH, and in soft or very soft water the pH will tend to be lower, though other things can impact this too.
So raising the KH without first raising the GH is not going to work. And once the GH is high (depending what it now is), the KH will correspond.