Mustard algae again

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PoolFrog

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Aug 9, 2013
130
Dallas, TX
A few weeks ago, we had what we thought was mustard algae in the shaded areas of our pool. The pool never failed an OCLT, so we went straight into an MA shock. We kept the FC at MA shock level for more than 24 hours, and during that time, we brushed, had Polaris running, threw all pool floats into the pool and laundered all swimwear. We did not backwash or clean our DE filter because we've only been in the house for about 3 months and have never done that before. We also didn't remove pool lights because they are in full sun areas, and we never saw the mustard algae in those areas. Everything seemed fine after the MA shock.

We're now seeing it again, and I'm now wondering if it could be living in the filter despite the MA-shock-level FC that passed through it for more than a day. I'm planning to do another MA shock, but do we need to clean the filter and replace DE this time? Would we be wise to keep FC at MA shock level for 2-3 days, or is that wasting bleach?

Below are my most recent numbers (TF-100):
FC 9.0
CC 0.5
CYA 50
TA 110
CH 770 (previous owner used cal hypo weekly)
pH 7.8

Any suggestions are appreciated!
 
If you truly believe you have MA based on what you see described on the Pool School - Mustard Algae page, I wouldn't try to do anything like run your FC at MA level for 2-3 days. MA (FC) treatment is a 24-hour thing. Simply follow the regular SLAM page first (link below). It may seem redundant, but that is best not only to validate the entire process, but the FC is at it's appropriate level based on your CYA. So if you find that you need to maintain a SLAM for a few days, the pool is still usable. As noted in the SLAM instructions, you should still clean the filter which will remove dead algae. Your light may be holding algae behind it - very common. Check any hiding spot. The MA should typically be in a shaded spot along the floor or wall. Before you start your SLAM, don't forget to lower your pH to about 7.2. If you have any doubt as to whether this is actually MA or perhaps something else in the water, get back with us and we'll discuss further. But stick with the established process (Pass a SLAM first, then MA level for 24 hrs) and it will work. Remember to be aggressive with your brushing as well. Oh, and don't forget water circulation. Make sure there are no bad "dead spots" where water can get stagnant. That happens often as well.
 
When you say to clean the filter per the SLAM instructions, do we need to disassemble the filter and replace DE, or do we just need to backwash? As I said, we've never attempted either one. We're on the fence about whether to try this ourselves or hire a professional to do it one time so we can see it demonstrated.

How can we tell if we have areas of poor circulation?
 
Just backwashing. But whenever you have a question about your filter, we can help with that too. As for the circulation, there are ways to see if your water is moving around well. One example is you could try dropping some packing peanuts or a couple ping pong balls in the water to see they get stuck in any areas. Some people find that useful as a tool to see if the return jets are moving water around well.
 
I never had any signs of mustard algae in my pool. Years ago, for the first time, I decided to open my light niches. Mustard algae galore. Your lights may be in sun, but the niches are not. I suggest opening them up and do a thorough cleaning!
 
Good suggestions, thank you. Do we need to backwash before we move into MA shock level, or after?

Our equipment appears to include a separation tank. As I understand it from doing some reading, this tank holds onto the DE that comes out of the filter during a backwash. Wouldn't that require us to open the filter and add DE to replace what was washed out? If it helps, we apparently have a Pac-Fab Nautilus NS48 filter if anyone is familiar with that.
 
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