At what FC level is it safe to swim?

[mgianzero]

I've shocked my salt water pool with dichlor to 22 for 3 days. All mustard algae is gone and FC seem to be holding at less than 0.5 ppm overnight.

Here's my results:

FC 20
pH 7.2
TA 80
CYA 70

It's now been two days since my end of shock and I notice the FC levels appear to be dropping about 5ppm per day as I am NOT adding any chlorine (thru SWG or dichlor) to get it back to normal levels.

Here's the simple question ... what is a safe level of chlorine (FC) to let my children swim in the pool again?

Sorry, but such a simple question and I could not find an answer with the search.
(Perhaps someone should post a safe swim level in a sticky note somewhere so anyone can look this up.)

Marc

 

[jblizzle]

Safe when:
FC is > the minimum and < the shock level for your CYA value, your CC is not more than 0.5ppm, you can see the bottom of the pool

Having the pH in range also makes it more comfortable.

shock level according to the Pool School chart is 28ppm or the calculator is 20ppm.

You need to maintain the FC above 5ppm at all times.

 

[Stuamurr]

Safe when:
FC is > the minimum and < the shock level for your CYA value, your CC is not more than 0.5ppm, you can see the bottom of the pool

Having the pH in range also makes it more comfortable.

shock level according to the Pool School chart is 28ppm or the calculator is 20ppm.

You need to maintain the FC above 5ppm at all times.

Nothing further to add than above +1

 

[mgianzero]

Sorry, but I don't follow what you said above.

Actually, before I shocked the pool, my CYA was low at 35 and I never had any measurable CC, but lots of mustard algae. So I used dichlor, which raised the CYA to 70 and my FC to 26.

Now my FC = 20. So that number is below the shock value (not sure if I should use 16 or 28 since my CYA was raised during the process) but above the minimum FC (which should be 3, right?). So is that considered safe to swim? In other words, what range for FC is it safe to swim in my pool?

 

[Stuamurr]

For a SWG Pool with 70 CYA, it is safe to swim with a Chlorine residual between 3ppm and 27.9ppm a Combined Chlorine of less than 0.5ppm and the ability to see the bottom of the pool.

Recommended levels are here: pool-school/recommended_levels
Chlorine/CYA Chart is here: pool-school/chlorine_cya_chart_shock
Information about shocking your pool is here: pool-school/shocking_your_pool
all of the above information is included in Pool School pool-school/

Mustard Algae (IF you really have it in your pool) is shocked at 41ppm with 70 CYA
see this thread:
pool-school/mustard_algae
and this thread:
chlorine-cya-chart-t2346.html#p18157.

You use the shock level for your current CYA level, disregard your previous CYA level of 35.

Regards
Stuart

 

[jblizzle]

Safe FC level is based on your current CYA. You said it was 70ppm. So the FC range is 5ppm to 28ppm like I stated.

Posted from my Droid with Tapatalk ... sorry if my response is short

 

[mgianzero]

For a SWG Pool with 70 CYA, it is safe to swim with a Chlorine residual between 3ppm and 27.9ppm a Combined Chlorine of less than 0.5ppm and the ability to see the bottom of the pool.

So what you're saying is it is always safe to swim in a pool as long as it is > 0.5ppm less than the normal shock value?

Mustard Algae (IF you really have it in your pool) is shocked at 41ppm with 70 CYA

Regards
Stuart

So, in other words, if I shock to mustard algae shock levels (41 ppm) I should wait until my FC levels drop below normal shock levels (28 ppm), in order to say it's safe to swim, correct?

I am pretty confident I have mustard algae. I live in southern California, the mecca for mustard algae. It grows mostly in shaded areas and the walls of the pool, but if I don't brush it (brushes very easily) it will spread to cover the whole pool eventually. It completely clears once I shock the pool, but if I do not brush it up from everywhere in the pool, it comes back. I think my problem in the past with shocking was I didn't raise it to high enough shock levels, and also test that all the algae is gone by measuring drop in FC overnight < 1 ppm. It also becomes much easier to treat in the winter months (pool stays open all year around) as the sun is not so harsh. I think all these signs tell me I'm really dealing with mustard algae and not pollen.

Last question is ... I have a variable-flow Pentair pump on my DE filter which accurately measures the pressure of a dirty filter. As long as I super shock the pool and my filter pressure remains low, must I take apart the filter to wash out all the grids, or will just a backwash get rid of all the dead algae? Once the algae is dead, it's not really a problem if there's a little remaining in the filter, is it?

Marc G.

 

[Stuamurr]

So what you're saying is it is always safe to swim in a pool as long as it is > 0.5ppm less than the normal shock value?

A. Correct, 30ppm is the "normal" shock level for your pool advised in Pool School, so 29.9ppm FC or less is suitable for swimming

So, in other words, if I shock to mustard algae shock levels (41 ppm) I should wait until my FC levels drop below normal shock levels (28 ppm), in order to say it's safe to swim, correct?

A. Correct, although 30ppm rather as 28ppm

Last question is ... I have a variable-flow Pentair pump on my DE filter which accurately measures the pressure of a dirty filter. As long as I super shock the pool and my filter pressure remains low, must I take apart the filter to wash out all the grids, or will just a backwash get rid of all the dead algae? Once the algae is dead, it's not really a problem if there's a little remaining in the filter, is it?

IMHO, no I don't think it is necessary, as you are running shock at 41ppm. I would make sure you pass the Overnight Chlorine Loss Test (OCLT) and that residual will run throughout your pool. A wee trick for you to give the filter a shock is to pour 2 jugs of bleach simultaneously into the skimmer so it gives the filter a good shock, I'm not so sure that's necessary in a DE filter (I don't know so hopefully someone else can firm up on that question for you) I dose Calcium Hypochlorite through the skimmer which allows the sand filter to fully dissolve the granules, and that also shocks the filter at the same time (I would point out though that it is not recommended to do this, but it works well for me in Scotland)

Regards
Stuart