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Question:
Is it safe to swim in a pool that has/is being treated for mustard algae? 

Response:

It's perfectly OK to swim in a pool that has been treated for mustard algae.

As long as the ph (7.4 - 7.6) & total alkalinity (about 125 ppm) are in balance & the 
chlorine level is under 3.0 ppm, you'll be fine. 

If there is still some mustard algae present, I would recommend laundering the 
bathing suits using a bit of bleach to make sure the algae is killed so as to not 
possibly contaminate another pool or spa.

Question:

I have a chlorine pool that I used YELLOW OUT to treat mustard algae. 
 
Although I thought that I raised the ph to 8.5 as instructed for YELLOW OUT usage, 

It appears that the ph levels were not sufficient. I am now having problems with
chlorine levels (tests read zero after shocking)  and it seems that I may have 
change the pool to a bromine pool from the addition of the Sodium Bromide 
(YELLOW OUT).  Is there a way to correct this to maintain a chlorine pool?  Or 
have I changed  the pool into a bromine pool?  

If so is there any problem with converting the pool to bromine and how would I 
do so...maintain the pool's sanitation?  I have bad mustard algae right now 
because of the low (actually none) chlorine levels.  How do you treat algae 
problems in a bromine pool?  My pool is approximately 28,0000 gallons.  

Thank you. Mark

Response

I'm sorry to hear about your troubles. Let's see how I can help you out. First, 
I hope you haven't added any more Yellow Out or sodium bromide product.

Often times (almost all of the time) when you have true mustard algae
outbreak - and yours sounds like a bad outbreak) - you WILL have a tremendous 
chlorine demand. Mustard algae is very chlorine & bromine resistant. 

When shocking, you MUST use LARGE amounts of chlorine as a shock. For
example, if you typically would use 10 lbs of shock in 20,000 gallon pool for an 
algae bloom, it would be very normal & very preferable to use 30 - 40 lbs. at 
one time when treating mustard algae - and MORE. Immediately after shocking 
you must vigorously brush the affected areas several times per day.  You also 
must maintain a HIGH (over 3.0 ppm) chlorine level and a normal pH of 7.4ish. 

Using BioGuard Optimizer Plus will help in preventing the recurrence (as long as 
you don't live in CA - the raw ingredient is mined in CA, but once it leaves the 
state, it can't come back!) BioGuard Banish will aid in killing it. AquaFinesse Pool 
Pucks will further disrupt the biofilm which serves as the "root base" for the mustard 
algae. There is no quick fix or silver bullet. Everything pool related must be 
treated; even certain poolside furniture where people may have sat or put 
there feet on with mustard algae spores. If you don't do this maintenance, it WILL 
be back next year or within months with a vengeance.

If this is the first time you have used Yellow Out or a sodium bromide product, 
then you should be OK as far as the bromine conversion is concerned. If you 
have used it multiple times, it's a different story.

If you can supply me with more information about the problem, including pictures, 
that would be a great help. Tell me more about the total pool picture, size, filter, etc.