The initial count of diatoms depends on factors like type of water body like artificial or natural , water present like RO treated or just filtered water in majority of aquariums were RO is used the diatom concentration and diversity is less when compared to ponds.
After dosing Nualgi as it doesn’t contain any live diatoms it can only trigger growth of diatoms present in the water so if there is more diatom diversity it can lead to more diatom count. In our research with lake water we are able to increase the number of diatom species from 8 before dosing to 30 after dosing over a period of 2 weeks and diatom concentration increased from 0.1×10^4 to 4.1×10^4 cells per ml per week.
Diatoms can be counted and species identification can be done by 10x100X magnification under microscope using identification guides and literature.
Yes the species of diatoms differ from salt to fresh water. Mainly in fresh water pennate forms like Nitzschia sp. , Gomphonema sp. and Navicula sp. dominate along with some centric forms like cyclotella sp. In sea water centric diatoms like skeletonema sp., Thalassiosira sp., coscinodiscus sp., chetoceros sp. will dominate along with pennates like Nitzschia sp., Achnanthes sp., Navicula sp.. In sea water we find more planktonic forms were as in fresh water there are more benthic forms.