How much have you played around with settings? If you have your 2D on switchfire max mode and sensitivity up you will see fine particles on screen. Also, with SI and DI the fish "dots" are not neccesarily going to correlate with what you see on 2d as far as size goes.
Also, on your DI/SI it looks like you may have your sharpness on which will show additional dots that can sometimes be mis-leading as fish.
No expert but have been playing around with my SI/DI unit for 2 years now and continue to fiddle with settings and learn little tweaks. Definitely the learning curve is worth it as it has helped me become a better fisherman.
I learned alot by watching videos from this website
http://www.technologicalangler.com/home He also has several free videos if you search you tube.