Will adding borax to 50ppm kill Mustard algae

[CarlD]

You know, you could simply take our standard route and raise your FC to shock levels and keep it there until your pool sparkles. Use bleach or Liquid Chorine for that.

First, lower your pH a bit to 7.2 or 7.3. Chlorine is more effective the lower the pH but too low has other issues.

Shock your pool with bleach until FC reaches 15ppm and keep it there, checking it twice or 3 times a day. Brush and vacuum your pool everyday.

Expect it to take a week to 2 weeks to clear. Since you haven't done this, I suggest you do this BEFORE you play with copper or bromine additives. Notice that after you use bromine, you have to use lots and lots of chlorine just to get rid of the "fix"--the bromine. IMHO, it's better to use the bleach to kill the algae.

My reason for this is we have a tried-and-true method that has worked for thousands of people. If it works, (and it usually does) then it's the easiest and most reliable way to clear your pool. If it doesn't work, then it's appropriate to seek more drastic measures, like the bromine algaecide or addressing the TDS or phosphate levels.

Once the algae is dead and gone and your pool is sparkling THEN you should add PolyQuat to inhibit further growth. It's sometimes called Mustard Algaecide, or black Algaecide--whatever. Look at the ingredients. The SOLE active ingredient should be Poly....<something long>..... 60%. Whatever they call it, if it's Poly....60%, that's PolyQuat.

If it were me, I'd raise the pool to 15ppm, add the entire quart, wait 48 hours, then check the FC (it will have dropped ALOT) and then shock again to 15, and consider it done. If it were me.

You can swim in the water at that level, but wear old bathing suits because they will fade.