New Salt System, algae is recurring regularly

[jhk49]

Shall I leave my SWCG "on" during the overnight test?

[SunnyOptimism]

No.

Since the overnight test is attempting to determine the loss of chlorine due to the organics and biologicals in the water (no UV degradation at night), you do not want a source of chlorine adding FC to your water. Just get the water up to shock level, leave the pumps running and turn off the IC40.

Good luck.

[Watermom]

If you lose no more than 1ppm of FC overnight and have less than 0.5pm of CC, we typically recommend one additional day of leaving the chlorine level high for added insurance and then you can let it drift down.

[SunnyOptimism]

If you lose no more than 1ppm of FC overnight and have less than 0.5pm of CC, we typically recommend one additional day of leaving the chlorine level high for added insurance and then you can let it drift down.

Totally agree with that! Thanks for the clarification.

[SunnyOptimism]

Shall I leave my SWCG "on" during the overnight test?

So what's up? How did your overnight tests go?

[jhk49]

As previously discussed, after adding the bleach to the pool at about 11:30am on Thursday and checking the FC at about 3:30pm, the level was 22.5 ...... then again checking about 7:00pm, the FC was about 22.0 (Thursday, 10/16/14). The pump ran all night and the recheck in the morning (about 8:30 am) the FC level was 19.5 (Friday, 10/17/14). I was concerned that the chlorine was not eliminating the organics, and the pool had somewhat of a green cast to it. I let the pool pump to continue to run until about 6:00pm and rechecked the FC which came in at 19.5 ppm. The pump did not continue to run last night but did kick on in the morning according to schedule, I checked the FC again (about 9:30 am on Saturday, 10/18/14) and it recorded as 18.5 ppm. And, the pool looked much better than previously, the green cast is gone.

The weather has been sunny but not real warm, mid 70's for the high and mid 50's for the lows. I am hoping that we have taken care of the problem. However, I am concerned with the differences in the FC during the overnight of the first comparison (between Thursday and Friday). Could the testing procedure at 10 ml sample provide a greater opportunity for error when using the titrate liquid and multiplying the result by 0.5 ppm? What do you all think?

[SunnyOptimism]

The 10mL test will have a +\- 0.5ppm error (Taylor error is basically +\- 1 drop)

However, you had an OCL (overnight chlorine loss) of 2.5ppm. Therefore, proper procedure is to immediately readjust your pool water back up to shock level and hold it there all day. If no one is able to test and adjust during the day, then you could go over the shock level by a few ppm's and then check again in the evening.

Basically you need to maintain shock chlorine levels until your OCL is 1ppm or less. I know it sounds tedious, and it is. Typically, the algae kill rate is high in the beginning and then the process tails off towards the end as your dealing with organic oxidation. It sometimes helps to backwash or clean the filter during this process to remove a lot of the dead algae (think of it as algae corpses rotting in your filter medium and emitting lots of organics into your water). Filter backwashing speeds up the tail end of the process which is the oxidation of organic compounds into volatile chloramines.

[jhk49]

Again, thanks for the info. I have just about run out of R-0871 but I have ordered some. Additionally, I am going out of town next week. So I plan on doing as much as I can this week toward solving the problem .... and, if need be restart in earnest upon my return.

[SunnyOptimism]

If your CYA is still in the low 30's, then use a float with 3" TriChlor tablets in it while you're away. Just make sure that the tablets are 99% trichlor and nothing else. It is perfectly OK to use trichlor with an SWCG. In my 16k gallon pool, three 3" trichlor tablets raise my CYA by ~8ppm and they take a good 10 days to fully dissolve from the float. Using that while you're away can help maintain some FC in your pool so you won't come back to as bad a mess if the algae starts in again. You can raise your FC above shock level before you leave with plain bleach and then throw the float in with a bunch of tabs and you should be good.

[Watermom]

If you are going to put some trichlor in a floater, make sure your pH is in the high 7s to allow some wiggle room for it to drop while you are gone. Trichlor is very acidic.