Mustard Algse - has no-one ever had this problem???

[kiwiswimmer]

I can not find two similar methods to kill Mustard Algae online and no-one seems to know anything on this forum - is it that rare? The pool place I got the algaecide and liquid chlorine suggested treatment should only take less than a day. Sites online suggest up to NINE days treatment. Anyone...Bueller...

[chem geek]

Yellow/mustard algae can be treated using chlorine alone, but requires higher shock levels with an FC that is 60% of the CYA level for several days after no visible algae. You also need to get behind light niches, under removable ladders, and put in any poles, or other equipment you use to clean your pool as well as toys (i.e. anything you put into the pool water) and need to clean your swimsuits in soapy water as well. Basically, you want to avoid any reintroduction of the algae back into the pool. This algae prefers shade which is why it often hides out in light niches and under removable ladders since it's not only shady, but the circulation is poor so it doesn't get hit with as much chlorine.

If your CYA level is high, then you should dilute the water first to lower it before doing a shock treatment. The typical products for treating yellow/mustard algae get around high CYA levels by adding things like sodium bromide which will turn your pool into a bromine pool where bromine is not moderated in strength by CYA. Some other products use ammonium to create monochloramine that similar does not get affected by CYA. However, it's the high CYA level that is the source of the problem in the first place and should be addressed since the high CYA level requires a proportionately higher FC level to have the same kill rates and most people don't raise their FC as their CYA level climbs. If you use products other than chlorine, then you not only spend more but they have side effects -- overuse of sodium bromide products will turn your pool into a bromine pool with higher chlorine demand.

When one is using only stabilized chlorine, such as Trichlor (or Dichlor), then one can easily build up the CYA level. The following are chemical rules of fact that are independent of concentration of product or of pool size:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

So even with a low 1 ppm FC per day chlorine usage, continued use of Trichlor will increase CYA by over 100 ppm in 6 months if there is no water dilution.

Read Defeating Algae and use the Yellow/Mustard shock level (FC that is 60% of the CYA level, but dilute the water first if the CYA is higher than 50 ppm).

[kiwipool]

Thanks Chemgeek. When I picked up the "mustard free", liquid chlorine and chlorine free shock (these are the things pool store said to use) they said just to brush, chuck it all in, put toys towels etc in and brush it again after an hour. I've done all of that and will wait untill the moring I guess to see if it may be working. I was a bit surprised to see my free chlorine at around 3 and total chlotina aroundonly 1 (note that I am using 3 year old test strips and this is only my second season with this pool). Should I be adding more chlorine? Thanks

[kiwiswimmer]

So I go out to the pool around 7pm (4 hours after starting this Mustard killing process) and whadaya know? My test strips show VERy low FC and TC???!!! I hope that there is a chemical/rational reason for this - anyone have any ideas? Cheers!

[chem geek]

Shocking is not a process where you dump something in and then leave. It requires a SUSTAINED high level of chlorine and in the early stages you need to keep adding chlorine, sometimes every hour or so since killing algae and clearing cloudiness consumes chlorine. You can only measure this accurately using a good test kit. You should either get the Taylor K-2006 kit here or the TF-100 kit here with the latter kit having more volume of reagents more intelligently organized so is comparably priced per-test.

You should be adding more chlorine though if your CYA (aka stabilizer or conditioner) level is very high, then a partial drain/refill is in order. But you really can't know any of this without accurate measurements and you can't get that from test strips. You can't even get it from most pool stores since most do the tests poorly, especially the CYA test. Again, get your own good test kit -- and make sure it's a FAS-DPD chlorine test. It costs more but is absolutely worth it as it will accurately measure Free Chlorine (FC) and Combined Chlorine (CC) separately to within 0.2 ppm or 0.5 ppm (depending on sample size) and doesn't bleach out and can measure up to 50 ppm.

[kiwiswimmer]

thanks. I am going to get a test kit. it's always going to hit the fan when the pool store is closed anyways. my cya (according to the pool store was 40 a few days ago. I just shocked the pool and show higher chlorine levels. I have no more commerical bags of shock or pool store chlorine. can I use household clorox if I see my chlorine level dive again? If so, do I just chuck it in the pool? Wow, so it was the process of killing the mustard algae that essentially gobbles up that chorine - wow.

[kiwiswimmer]

OK, so I am using the handy dandy pool calculator and I'm about to add 26oz of clorox - I have a 12500g pool and my crappy test strips are telling me that my FC is about 2 - I'm going to see if I can raise it a bit.
One mistake I made in hindsight is that I started this process at 3pm on a 82F sunny day - maybe thats where some of my chlorine went eh?

[chem geek]

If you have CYA in the water then you probably didn't lose more than half the FC due to sunlight -- the rest was killing algae. If you have loss overnight, then that's due to killing algae and/or clearing dead algae. And yes, you can use 6% Clorox Regular unscented bleach. You could also use 10%/12.5% chlorinating liquid from your pool store or hardware/big-box store.

[kiwiswimmer]

I took at water sample in to the pool store this morning. My chlorine was again low so they suggested shocking. I did first thing but afer a couple of hours FC was low again. I just shocked it again. They suspected high phosphates (we live pretty close to farms) at 300. i put a half of a bottle of some very expensive stuff that is supposed to get rid of the phosphates. Do you think that will help my FC issue in the near future?

[chem geek]

I've had 2000-3000 ppb phosphates in my pool yet kept it algae-free by using chlorine alone at the appropriate FC level relative to the CYA level. So the short answer is no, a phosphate remover won't clear your pool but it will take the edge off of algae growth. You kill algae and clear a pool using a shock level of chlorine -- an FC of around 40% of the CYA level.

Shocking is not a one-time event but a SUSTAINED high level of chlorine.

[kiwiswimmer]

Thanks again chemgeek. That phosphate reading was actually 3000. I backwashed this morning and it looked like milk!

[chem geek]

Yes, that is the phosphate remover (lanthanum chloride or lanthanum carbonate) combined with phosphates and carbonates getting backwashed.