Dead algae recirculating into return lines

K-Tanz

Member
Apr 18, 2018
9
Phoenix/AZ
Hey everyone! I have an issue with dead algae being recirculated back into the pool. I know this problem could be avoided by just keeping the pool algae free and not having to bomb the water from time to time, but here we are.

It's a brand new sand filter, a TR100, with brand new sand. The pump is an old workhorse that I don't know the real details of. It's a 28k gallon in ground plaster pool. The system used to have jets, but I pulled all the jets and am now running a 4 wheel Hayward Aquanaut, so the jet holes are now serving as the returns. It recirculates so much sediment that when I turn on the pump I can watch the returns pump gigantic clouds of dead algae into the pool, turning a relatively clear pool into a turbid cloudy mess.

Can this be caused by cheap sand? I am suspicious that the company who installed the filter used very cheap sand as I sometimes notice filter sand at the returns. When I backwash I definitely get lots of nastiness out of the filter, so a filter deep clean is in my near future plans. My only other thought is regarding air in the system. I definitely have an air leak I need to chase down that sends air through the returns. Perhaps air running through the filter forces debris back to the return side? I didn't think the air leak was a big deal and my pool guy told me to not worry about it so I haven't taken the time to really diagnose it.

Any suggestions beyond deep cleaning the filter would be much appreciated.

Cheers!
 

K-Tanz

Member
Apr 18, 2018
9
Phoenix/AZ
Oh there's live algae no doubt! I am not fooling myself about that. I am comfortable hitting it with the Slam and have no issue killing the algae. My bigger question is whether it is normal to get those fine particles recirculating back into the pool, or if it's really just an issue of needing to be more diligent with the algae prevention.

Thanks for the reply! I didn't know there was an option to add DE in with the sand, very cool!
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,834
Laughlin, NV
You add DE to the sand filter. Essentially making it 'dirty' so it will filter better. Always wait until the pressure rises by 25% over clean pressure when backwashing a sand filter. If you add DE, when you backwash, you have to add more, as it is disposed of during the backwash.

You said this new sand, correct? If so, channeling should not be an issue.
 

mariane

Bronze Supporter
LifeTime Supporter
May 8, 2012
1,096
Southeast Michigan
Are you seeing sand on the bottom below the jets/returns after the cloud settles or settled dead brownish looking algae? Did the PB use pool filter sand, or maybe the wrong type of sand? Is the SLAM not killing the algae?
Inquiring minds want to know. :scratch:
 

charlieTX

LifeTime Supporter
Apr 22, 2013
68
As mentioned in reply #3 it sounds like an air leak could be causing you to lose prime at the pump which lets the water drain back from the DE filter, through the pressure lines and back in to the pool.

Check the lid on the pump basket for air bubbles and look for where air is entering the system, most likely need a new o-ring and lube on the pump basket lid or a replace the flap on a bad check valve. Could also be old diverter valves or old unions sucking in air. Listen and watch for leaks around the equipment when you turn the pump on and off.

If you don't have a check valve on the pressure side you should add one to stop the water leaving the pump basket after the pump shuts off.