I haven't checked my fuel for algae as it's been parked for 14 years. I just noticed when I moved it last summer that the fuel was very dark. Could just be from age. If it is bacteria causing the colour change it would eventually clog the filter.

I haven't used the additive because it's just not an issue in an automotive application, especially when you burn 100 gallons or more a day and use quality fuel.

Is yours a 12 valve or a 24 valve? 24 valve engines all use an electric lift pump to move fuel from the tank so you could just keep cycling the key to prime the fuel system after a filter change. 12 valve had an engine driven transfer pump as far as I know, at least on Dodge trucks, so you would need a jug of fuel to fill the filter with. No reason you couldn't do the same with a 24 valve to speed up the process.

Kevin