Dear Tomasz,

Please have a look at this useful PDF attachment.

Good luck!

Dear Tomasz

The suitable method for determining the algal biomass without scraping from the solid substratum could be estimation of dry weight of the solid material initially and finally after algal growth. The difference will give you the algal biomass.

For what purpose you need to estimate phosphorus? I think in order to do it, you have to take certain amount of algal biomass, digest and estimate phosphorus content present by spectroscopy.

I would add a sacrificial piece to the substrate and measure wet weight before after submersion and waterlogged - then measure after allotted time, subtract initial weight. Then multiply that by dimension of actual substrate. You could do this daily to determine rate of growth.

Thank you for all great suggestions. I will try to check your ideas with determine mass differences.