I thought I had it bad last week!! I'm so sorry! My problem was about 1/3 as bad..it was a freshwater tank though!
My problem was too much light and too little
CO2 for my lightly planted tank....
I would guess Lighting would be the main issue as you have no fish and are not feeding much (but I would cut out for a while...your snails, crabs and shrimp must feel like they got locked up in a grocery store will all that free floating algae to eat).
What wavelength is your light at? Not being able to tell real good (due to the green) it almost looks like perhaps you have a freshwater bulb (5000-6700k) wavelength light perhaps? I think that could encourage some algae growth.
I agree with lights out and covered for 3 to 5 days.
I got a Diatom Filter for my problem, as my 1 and 3 year old would not handle a blackout period. I got the Aquarium Products Sytem 1 Diatom Filter for $110 and Big Al's
www.bigalsonline.com. In 4 hours...my 90g
FW tank was clearer than any tank I have ever seen. It was amazing. This is a short term fix though...you need to find out what is causing it. Also...some would say that diatom filters may filter out too much of the "good stuff" that marine aquariums need.
As your tank is relatively small...there is a cheaper Diatomic Filter...The Vortex. It is like $50-60 at Big Al's. A lot of people have also had good luck in using a Magnum HOT canister for $40 using the Micron Filter (which I belive comes with it) alone, or some people even add DE to that (but some have got a tank with a white cover of DE if it is not done correctly.)
Another thought is the distilled water...I know NOTHING about this yet...but some people say the just distilled water could be bad...and that
RO/
DI water is better..but I will leave that subject for the more experienced.....
Good luck..I feel for you! You spend hundreds (perhaps thousands) of dollars for an aquarium..and you get a gross, green mess...I was there with you last week!