Not filtering correctly

sounds like the green algae is going straight through the filter and back into the pool.
If its a cartridge filter, you possibly need to hose all of the existing sediment out of it.
If its a sand filter, you most likely need to backwash the filter.
I would also recommend vacuuming the green algae to waste if there is the capability to do that on your system.

Have you backwashed the unit? That would clean out remaining algae.

Always vacume on waste when you have algea shock at night always

I think Brandon's answer deserves a little more time and a slight explanation... as I think it is Spot On!
Algae dust is usually "Already DEAD" algae!
And normally it is way to Small & Fine to be trapped by the filter.
We here on this forum do not know what type of filter you have, But if you do have a "MultiPort" valve as Brandon suggested you turn to the "Waste" mode, you will not use the filter mode to vacuum, as this will only BLOW the Fine Silt like substance right back into your pool, spreading out into the water to be suspended turning your water cloudy if not green, until it settles, and once again you have a covering of Dead Algae Dust on the floor of your pool. But when the filter valve is in Waste mode, you will bypass the filter and the return line altogether and your vacuumed algae silt will be sucked up into the valve, and OUT the valve to waste. And just like that all of the algae dust is vacuumed out and did not Blow back into your pool.
I just had a situation where we cleaned up such a pool where the customer couldn't get the algae out, we came out and vacuumed to waste. And I by chance took a picture of the partially vacuumed pool and Dust remaining.

If you don't have a multipart valve, then if the pool has no debris but only dust, then and ONLY then, should you use Backwash mode. You NEVER want to vacuum a pool with debris in Backwash mode! NEVER!!! Because the larger debris you are vacuuming will get caught in the internals of your lateral drain assembly or your DE Grids. then it will be very difficult to un clog them, which in turn will reduce proper water filtration efficiency! But the algae dust will be able to pass right on thru. If you have neither of these types of filters because you have a Cartridge style filer, the elements may be able to trap the dust, if it is still to fine to filter, you obtain an additional pool pump, place it pool side, and in the pump out the pump will be two vacuum hoses and away you go.

Good Luck

Get ready for a full weekend of cleaning your pool :) This is the chemical free method...
1st... Start with a clean filter...So clean your filter...
2nd.. Vacuum your pool and get most of the algae up from the bottom and sides.. Go slow so you do not stir up the algae. Make sure you use the vacuum attachment with brushes..
3rd..Clean your filter...
4th...repeat step 2 again...
5th... Clean your filter...
6th... Brush your pool with a pool brush to loosen the remaining algae..
7th... Set your pump timer for 12 hrs and your chlorinator for 10 to 11 of those hrs... and run for 3 days...
8th.. Check your water and see if has cleared and the algae is almost completely gone.. If so, check your free chlorine level and adjust your cycle down if at the required level..
9th.. if your chlorine level is not at optimal, run at the 12 hr cycle for 3 more days and check..
10th.. After water is clear and free of algae, clean your filter and adjust your cycle down to control your free chlorine level...
Good luck and hope this method works for you.. It has for me for over 2 years with my Intex Salt Water system...
Please take the time to rate me and write a comment... really appreciate!!!

You don't mention the size of the pool. If this is a above ground small pool ... dump the water, clean the liner and refill it. Remove the metal with a sequestering agent. Get the alkalinity correct. Get the pH correct then add the salt to 3200 ppm.

Chlorine kills algae. Are you sure it is algae and not metal in the water?

pH should be 7.2 to 7.6. Alkalinity should be 100. If a gunnite pool, the calcium should be 300. Salt should be 3200. Cyanuratic acid should be 50+ if this pool is outside (not indoors).

What to do. If this is a big pool, and you are sure this is not metal in the water, I would super chlorinate the pool - take it to 20 or so ppm. Run the filter for at least 24 hours. Watch the pressure ... you will be filtering out a lot of stuff.

Let me know what happens ...

Thanks for your question @ FixYa.com

if the debris your are trying to vacuum up is more fine than the sand can catch (specifically with algae or dead algae), it will blow right through the filter. there is a setting on your filter called either drain or waste. when using this setting the water completely bypasses the sand and comes straight out the back wash outlet. this is a rather tedious task as you lose alot of water, but it is the only way to remove this type of particulate. make sure the pool is overfilled when you begin. good luck!

As in most cases today, pumps and filters are not properly matched. The filter cannot retain such fine algae particles because they are being driven through the sand bed by an over zealous pump. I suggest that you let the dead algae settle to the bottom. top up water and use the vacuum to waste position on m.port valve. Vacuum in such a way that you dont stir up the debris.

It could be that there is algae growing inside the tank of the filter. You may want to vacuum to waste to get the algae out of the pool and clean out the filter. If you have a Cartridge or DE filter, you will need to do an acid bath for the grids. Take the internal parts out of the filter and clean with bleach water, use bleach water on the tank also.

If you have a sand filter, you will need to empty out the sand, clean internal parts and tank with bleach water then fill with new sand.

DE filter? If so then you need to give the filter an acid bath to purge the dead alge from the filter (Fingers, Grids or Discs). Go with 1part muriatic acid to 3 part water. Let soak overnight. The water should turn almost neon green.Rinse off and reassemble. SHould be Good to go. DE and Cartridge filters should be given an acid bath once a year.