Small Spots of Algae

[rjledoux]

First post but I've learned a lot from this board.

Today I noticed a small spot of algae and need to start the shock process.

Since I know I'll be asked ....
FC 6.81
TC 6.91
PH 7.6
TA 97
CH 166 *was next on the list to deal with
CYA 45

I have a very high exposure to UV and normally use a LOT of bleach. I am converting to SWG (I have it but haven't installed it yet).
I know my CH is low so would this be a good time to break from using Liquid Bleach to shock and use Cal-Hypo? and/or Dichor? My CYA is too low for a) my UV exposure and b) installing the SWG.

Water still looks crystal clear but I had a several small spots of algae on the wall. The water has never fallen below minimum FC.
Thanks

 

[JasonLion]

Welcome to TFP!

Assuming you have a plaster pool, you do indeed want to get your CH level up. Since you need to SLAM the pool anyway, cal-hypo is a reasonable way to approach things. However, if you do go that route, keep an eye on your CH level and make sure you don't overshoot.

I don't recommend using dichlor, it isn't nearly as good a deal overall in this situation. First, it will lower the PH dramatically, which will require compensating additions of soda ash (or a combination of borax and baking soda). Second, you don't want to raise the CYA level until you are sure you have taken care of the algae. Getting rid of algae is much easier at your current CYA level than it will be at higher CYA levels.

 

[chem geek]

Those numbers look like they are coming from a pool store. Just because they use two digits after the decimal point doesn't mean they are accurate. I strongly recommend you get your own test kit, either the TFTestkits TF-100 or the Taylor K-2006 (see Test Kits Compared). This will not only give you better accuracy, but save you trips to the pool store.

If the numbers are from your own test kit that is a DPD test using a colorimeter, I'd still get the FAS-DPD test for confirmation. You can also get CYA Standard Solution (most important), CH Standard Solution (next important), and TA Standard Solution to validate the accuracy of your instrument. The CYA test is often inaccurate and the CH test is often off if the CH is high. This is all why we just recommend the test kits we do since we know they are accurate and consistent.

 

[harleysilo]

Today I noticed a small spot of algae and need to start the shock process.
Water still looks crystal clear but I had a several small spots of algae on the wall.
The water has never fallen below minimum FC.

One of these statements doesn't belong.....

Could you fill out your sig line so we know what you have/dealing with. I just wanted to make sure you bought a large enough SWG for your pool. Just saw another thread where a person is obviously struggling to keep FC levels appropriate and their SWG is running at 95%.....i only mention this cause you say you haven't installed it yet and am wondering if it is returnable if horribly undersized.

 

[rjledoux]

The numbers are from my own test kit that is a DPD test using a colorimeter, specifically then Lamotte 2056. Resolution on cholorine is .1 ppm +/-2% from 0 to 10ppm.
Picking up a 2nd test kit is probably a good idea.

The SWG is not yet installed. I have ~18K gal. plaster pool the SWG is a Pool Pilot Digital Nano Plus with a RC-28 manifold. The cell in the RC-28 manifold is capable of producing 1.06lbs of chloriene per day.

I noticed the quarter size spot of algae while performing routine brushing. Upon closer inspection I found a couple more. I've been using higher than normal amounts FC but I wrote it off to the south Texas sun and the non-stop debris that litters my pool. An OCLT is sometimes difficult because of the debris (pine needles, pine bark & pine cones) even if I vacuum the pool before the test at night, before morning there will be organic debris in the pool.

I'll update my signature.

 

[chem geek]

You might take a look at circulation in the pool and reorient the returns (if they are movable eyeballs) to help redirect flow to areas of poor circulation, if possible.

 

[rjledoux]

also of note

When I took ownership of the pool CH was normal and CYA was off the charts (best estimate I have is ~160). Both of these dropped predictably with a partial drain. The partial drain was to drop the CYA low enough to be able to SLAM for the mustard algae the previous owner left as her parting gift to me. It is highly unlikely that the CH is reading inacurately on the Lamotte because it's over 400ppm. The algae I have now is not mustard algae.

 

[rjledoux]

You might take a look at circulation in the pool and reorient the returns (if they are movable eyeballs) to help redirect flow to areas of poor circulation, if possible.

You may be on to something here. All of the spots are in an area of the pool without a return. It was meant to be serviced by a waterfall which has a leak and hasn't been used. I'll pull a couple of samples from that area and compare with an area around a return.