Mustard algae appears right after filter pump is started

[Mark123456]

We have an above ground 48" x 18' pool that gets mustard algae on the bottom of the pool (looks like sand) but only if we run the pump. We have repeatedly shocked the pool used chlorine on the ladder and any floats in the pool, took the hoses off the pump and chlorinated them also. We change the filter weekly. Went to a pool store with a water sample and all values were within specs, they are befuddled also. Shocked it again 2 days ago, left the pump on for 24 hours by the end of that the bottom had loads of algae.

1. If we leave the pump off for several days we see almost no algae.
2. If we put the pump on within 10-15 minutes we see the algae on the bottom.

Any ideas or suggestions?

 

[tensec10]

What type of filter? Sure its not sand?

 

[Mark123456]

What type of filter? Sure its not sand?

No it is not a sand filter just a paper cartridge that we replace.

 

[zea3]

Hold a sock over a return and turn on the pump. Collect the material in the sock and turn the sock inside out on a piece of white paper, take a photo and post it here. What you are describing is not how algae grows.

What are you using to shock the pool? Do you vacuum the pool?

Please edit your signature with information on your pool, such as pool type, material, and size in gallons/liters, pump brand and size, filter brand, type, and size, any additional equipment such as heaters, in floor cleaners, automation system if any, extra features such as bubblers, deck jets, fountains, waterfalls, ect. This information will help us answer your questions.

 

[Mark123456]

Per the recommendation i put a large white sock over the return and ran the pump for about 10 hours. The sock is slightly grayer but i do not feel any sliminess or any different feel to the sock.I have enclosed a photo. But here is the really odd thing no mustard algae on the bottom of the pool (assuming that is what it is), without the sock it would have a bunch to vacuum up after 10 hours.

Perhaps the sock is catching some microscopic stuff that is causing this issue? Not sure leaving the sock on is bad for the pump?