Mustard algae and cloudy water


New member
Apr 5, 2017
Fort Lauderdale
Hi there,

I'm looking for direction on how to work my pool back to cristal clear again. About 2 weeks ago, I cleaned up the pool very well (it had minor hints of green algae on the water but nothing too serious since my pump was off for a couple of weeks), balanced my chemicals (I used the 5 ways test kid HDX from Home Depot) and after a few adjustments (added liquid chlorine and muriatic acid) the levels were perfect: 2.0 Clorine, 7.6 PH, 110 Alkalinity, and the pool looked gorgeous.

Then after a heavy rain and some strong winds about a week ago, the water started to look a bit cloudy. I must add that I made a mistake by using rain water I collected in a cylinder (for watering my plants) and used it to get more water in the pool to avoid using expensive city water -i've done it in the past, but I usually put chlorine in it abut 12 hours prior, but I didn't the time). The next day, I started to see some brownish sediments on the walls and on the bottom of the pool that at first I thought it was Polen from the Trees (I have 2 big mango trees flowering right now not too far from the pool) but after making some thinking I noticed that I didn't see any of this 'polen' anywhere else (I should be able to see it on other surfaces, right?) and that is when I realized, after doing some internet research, that I have mustard algae. I took water sample from the skimmer and 'cultivate it' for a day, and noticed how this was growing in the glass cup.

So, what I did next was to clean the pool with the brush, run the pump with filter and vacuum and add a bit more of chlorine. The water cleared up from the mustard/brownish residue but was cloudy. I open the filter housing to clear the filter and found the filter to be completely covered with green, brown residue- and i was so surprised since i have cleaned it up not over 10 days before that). So i clean it thoroughly, first with the water whose, then with some chlorine and let it sit for 10 mins, rinsed it with lots of water, clean it in a bucket overnight with TSP (1.5 cups on 5 gallons of water) and let it there for 12 hours, rinsed it very well again, and then let it sit in a mix of water and muriatic acid for other 5 hours (5 gallons of water and 1/2 muriatic acid). Afterwards, I rinsed the filter with lots of water and pressure (didn't use te pressure machine, but only the hose at the fast setting). Placed the filter back and run the pump.

At this point, my water was still the same, cloudy, no settled algae or particles, but the water was not that 'sparkling blueish color' rather a pale greenish one.

Run the filter for 24 hours, rinsed it with water, some debris came, but nothing mayor. Kept on running it for 12 hours and no change was noticed.

I read the chemicals again with the 5 way test kit and the levels were Ok. 2.0 to 3.0 chlorine, PH was up bit to 7.8 (so I added more muriatic acid to take it down). Read the test again a couple of hours later and the level on the PH went down to 7.6.

Then that night, I went to the Home Depot and purchased 2 gallons of Chlorine, and 1 32 oz bottle of Clorox My Salt Pool all Purpose Algaecide (copper based) and followed the instructions. First I checked chemical and I was 7.6 PH and 2.0 Chlorine, then I added Chlorine (2 gallons, and waited 2 hours. I did brushed the pool while I waited, and once it was all done, I added 20 oz of the algaecide and made sure it was well distributed. I brushed the pool lightly again and let it work. Pump was running this whole time.

Next day in the morning I noticed a little change, water was still cloudy, and with this mate dull greenish color. I cleaned the filter, spray washed it and apply some chlorine to it, cleaned the housing and the pump very well and let the pump run 24 hours. Changes were not that noticeable. I took the water to the pool place nearby (Pinch A Penny) and the results they gave me were Total Chlorine: 3ppm, FC: 3ppm, Combined Cl: 0, PH 7.8, Acid demand: 1 (HIGH), Total Alkalinity 105 ppm, Calcium Hardness 225 ppm, Stabilizer: 60 ppm, Salt: 2,850 ppm.

That night (24 hours after I applied the algaecide) I did a shock to the pool. Chlorine was 2.0, PH was high again at 7.8, so I lowered it and waited for it to mix well and active for about 3 hours. measured it and it was back at 7.2-7.6. And then I brushed the pool and applied 2 gallons of Chlorine, and run the pump (never stopped it actually), sprayed cleaned the filter and went to bed.

Yesterday morning the pool had turned from that greenish dull color o a blueish color, but still cloudy -see pic attached for before and aftert- I've been vacuuming and brushing the pool twice a day, the same with spray washing the filter, my 5 way kit showed me I have way over chlorine (got an orange-almost reddish color), and the PH was back at 7.8. I also took a water sample to the pool place and their results were Total Chlorine: 8.0 ppm, FC: 8.00 ppm, Combined Chlorine: 0 ppm, PH 7.8 (High), Acid demand 1 (High), Total Alkalinity 135 ppm, Calcium Hardness 255ppm, Stabilizer 35ppm (way lower than the first time).Salt 2,900.

I've been running the pump this whole time (ove 3.5 days now) non stop in super chlorinate, and rinsing the filter 2 times a day. The store told me to add more muriatic acid and stabilizer, but I wasn't sure about it, I made my reads with the 5 way test kit and got my PH to 7.6, and added a little bit, so It lowers the acid and the chlorine can work better. And after deep brushing the pool 3 hours after I popped the muriatic to bring it dow, I brushed the pool very well, and apply one extra gallon of chlorine.

This morning the pool seems a bit less cloudy by but not too much, still with the blueish color but the cloudiness is driving me nuts. I see some areas where I could brush stronger but its just very faint.

So, my question what should I do now? After lots of reviews online, I see that SLAM the pool is the next step. Should I do follow this? Should I do add the stabilizer as recommended by the pool people? I just don't want to add more chemicals if not necessary and neither want to mess up with the chemical balance of the pool. My last read is lots of chlorine (almost orange/redish) and the PH is 7.2-7.6.

Should I add the stabilized and do the SLAM (Adding tons of chlorine)? please let me know. I'm also concern about the pump running for so long non stop (except when I cleaned the filter).

Thanks in advance!

Sorry if any typos. Best,




Mod Squad
LifeTime Supporter
Jan 17, 2012
Evans, Georgia
Your 5 way test kit hinders you greatly. The FC only reads to 5, right? And I don't see a CYA test mentioned. Your FC may be entirely too low for your CYA.

We need to know:

and all from one of the accurate test kits we trust. EIther the TF-100 (most popular) or Taylor K-2006 (no other number kit) .
Either of these can be obtained via: Amazon, or The fastest is form

While your pool is looking better in the right sided pic, its still hazy.

Rain water is ideal in pools. It won't cause problems but if your FC is too low anyway....

Algaecides do NOT kill algae (shocking news, I know) but its rare use is as an algae preventing agent in an otherwise algae-free pool. That you used one with copper is unfortunate as copper causes stains.

I would also advise you to avoid buying chlorine at Home Depot or Lowes as they store it outside in the heat and sun which weakens it quickly. Buy from Walmart or a store that stores it inside and has a lot of turn over. I like Costco myself. Walmart sells 10% liquid chlorine in the pool department that is sometimes cheaper than the 8.25% bleach they sell in the laundry aisle.

So the bottom line is you need to SLAM. You also need a better test kit for said SLAM.

Yippee :flower: