Low Ph, High Ta, High Cya, Chlorine Not Holding

[dulac87]

I have a 30,000 gallon plaster pool with a DE filter and am having trouble bring the water into balance. The initial problem I found is that the pH was low (7.0) and the TA was high (140). I have also found that the chlorine is not holding and, upon testing today, the CYA is very high (>100). For the chlorine, I have been adding 2-3 12 ounce cups of Chlor Brite granular every day. Typically, in the heat of summer, I would be doing this every 2-3 days.

Since reading several posts yesterday, I have been aerating the pool with a hose running from the filter and have added a box of 20 Mule Team Borax in an effort to drive the pH up before adding muriatic acid to bring the TA down. As of now, my readings are:

TC >5

FC >5

pH 7.2

TA 180

Cal Hard 400

CYA >100

On the pH/TA front, I am going to bring my air compressor out to crank up the aeration. What else should I be doing?

I am at a loss on the CYA. Thoughts?

Outside of the wacky readings, you would never guess there was anything wrong - the water is crystal clear.

[chem geek]

You have several separate issues. Most likely your high CYA level is making your chlorine level ineffective against a nascent algae bloom you are fighting and this is consuming chlorine at a far faster rate. Unfortunately, the only way to lower the CYA level is a partial drain/refill with fresh water. This will also reduce your CH and TA levels unless your fill water is high in both, but again you don't have any choice to deal with your high CYA level. In the future, monitor your CYA level and stop using chlorine sources that contain CYA (Trichlor tabs/pucks and Dichlor powder/granules). With your high CH, you should also avoid Cal-Hypo as a chlorine source. That leaves sodium hypochlorite as either chlorinating liquid or bleach and the expensive lithium hypochlorite.

For lowering TA you NEVER add Borax or anything else to make the pH rise. Adding acid will NOT lower TA by itself. Acid lowers both TA AND pH while base raises both TA AND pH so going between acid and base simply yo-yos not getting you anywhere. Only aeration will cause the pH to rise without any change in TA so the following procedure is the correct one to use for lowering TA (but in your case a partial drain/refill to reduce CYA should be done first).

ACTIVITY .......... pH .... TA ... In your case (assuming 6.8 is the lowest measurement on the pH test kit)

==================

Acid ..................... - ........ - ... Add enough acid to bring pH down to 7.0 (if it's already there, then just skip to the next step, aeration)

Aeration ............. + ....... 0 ... Aerate until pH rises to 7.2

Acid ..................... - ........ - ... Add enough acid to bring pH down from 7.2 to 7.0 (you may continue to aerate while you do this)

---------------------------------

Aeration & Acid .. 0 ....... - ... Continue this combination (cycling of the two above) until TA is at the target you want

then AFTER you have reached your target TA,

Aeration .............. + ....... 0 ... Aerate until the pH rises to your target pH (say, 7.5).

==================

Net of Above ....... 0 ........ -

Note that there is NO addition of base (Borax or otherwise) in the above procedure. Aeration would include running your SWG, running your waterfall, adding any fountains or other aeration features, getting an air compressor with a nozzle that produces tiny bubbles and putting that in the deep end of the pool, etc.

Again, in your situation with very high CYA you should probably do a partial drain/refill first since it would take extraordrinary amounts of chlorine to prevent algae in your pool. If you want to prevent algae without the high chlorine level, then you can use PolyQuat 60 algaecide, but would need to use a maintenance dose of it every week until you got your CYA reduced.

[dulac87]

What percent of the water should be drained for a partial drain? And what is the risk to holding off addressing the CYA issue for five days? We have a couple of end of school parties early next week and I am trying to gauge what level of effort needs to take place this weekend.

[chem geek]

If your CYA is truly at 100 or more, then a partial drain/refill of half the water would give you 50 ppm CYA or so. It all depends on what "100+" means. If that's really 200 ppm CYA, then you'll need to replace most of your pool water. If you do the drain/refill through continuous draining while simultaneous filling, then it will take more water -- about 69% of your pool's water volume to dilute 50%. If you use the sheet method where you take a large plastic sheet to cover your pool and fill fresh water on the top while draining from underneath (the plastic sheet will drop into the pool separating the two layers of water), then it would take 50% of your pool water volume to dilute 50%.

Yes, you can wait on this, but I suggest you add PolyQuat 60 algaecide right away as a preventative. That will at least keep algae away. This may help hold the chlorine a little longer if the algaecide helps stem some of the algae growth, but you will still need to try and maintain some chlorine levels even when using the algaecide. You could readily try and maintain 10 ppm FC, but it sounds like you don't have a good test kit and should consider buying a Taylor K-2006 (see this link or the equivalent Leslie's Chlorine FAS-DPD Service Test Kit (see this link. Even if you kept 5 ppm FC with the algaecide, that would be OK for the short-term. You could still end up getting an algae bloom if your nascent algae is about to boom, but generally the water will look dull or cloudy first before it turns into a green mess.

[waterbear]

Chlorbrite is dichlor. It will keep adding CYA to your pool as long as you use it! For each 1 ppm of FC it adds it is also adding .9 ppm CYA! You need to switch to an unstabilized chlorine right now! Based on the fact that your calcium is high I would use either liquid chlorine or the expensive lithium hypochlorite.

[dulac87]

Thanks for all the help. I drained half the pool late last week and am back up already. The CYA is down to 90 (so, it was a little high). I plan to take the water down each week when I backwash and then refill with tap water so that I can get the CYA down further.

I have also switched to liquid chlorine. How much and how frequently should I need to add liquid chlorine in a 30K gallon pool?

[chem geek]

If your pool is in full sun, then probably every day unless you have a pool cover in which case it will likely be 2-3 times per week. Just make sure you maintain a minimum FC level appropriate to your CYA level. At 90 ppm CYA, you need at least 7 ppm FC in your pool at all times to ensure your pool does not get algae.