Dear N.T.,

You can find the answer in:

https://www.researchgate.net/post/How_to_calculate_the_concentration_of_spores_in_a_fungal_spore_suspension

Good luck.

Agree with Brain comment, also, if you do not like to use haemocytometer, make spores suspension and take about 0.2 ml and spread over fresh sterile culture medium and incubate, then count CFU. This will give you the actual living number of spores

Nothing to add to what Brian and Yehia have said, apart from the fact that I would not think ultra pure water is necessary - sterile H20 should be fine. As you don't know the initial conc. 0.2 ml might be too high or low to give a sensible cfu count, so plate out a range of 2-3 10-fold dilutions.

My dear friend: why do you not try to do some data mining from the literature available. I would suggest that you use simple saline solution (0.85% NaCl) with a drop or so of a surfactant like ofTween 20 or Tween 80(would do ) per 5 ml. Use such a medium for serially diluting the spore suspension of A.niger and keep checking the spore count using a suitable hemocytometer like Neubaur's chamber.