Advice Needed - High CYA, High Nitrates, and Lots of Algae

Hi Folks,

We live in Southern Maryland and have the following:

20' x 48' gunite pool
36,000 gallons
Jacuzzi tri-clops filter
Jacuzzi pump (3/4 hp I believe, I can confirm this if important)

We had a local pool company open the pool June 15; the water was clear, but there was a heavy algae growth on all sides and bottom. They added 5 lbs of dichlor at opening; we have used dichlor as our pool shock for several years with no problems. I put two 3-inch chlorine tablets in each skimmer and brushed the pool. The walls came clean but the water turned into a green mess.

I have been running the filter 24/7 and have had to clean the filter cartridges after 12 hours of filtration due to pressure going up 10psi (filter cartridges are covered in algae each time I changed them). I have 2 sets of cartridges, but it is a pain to change them out and clean the cartridges 2x a day.

The water stayed green through the weekend and we had the water tested June 18. The CYA was over 160 and I was told to drain 60% of the pool and refill with fresh water. We are on a well, so there is no way I could drain that much water at once, so I have drained about 2 inches of water the past two evenings and and added water via the hose to replace.

We had the water retested today; the pool company did some additional tests and here are our results:

free chlorine - 0.37
total chlorine - 0.88
combined chlorine - 0.51
ph - 7.47
hardness - 161
akalinity - 115.03
CYA - 163.62
copper - 0
nitrates - 80
phosphates - 50

The test printout today recommended a 90% drain of existing water and replacement with fresh water.

Is there anything besides a full drain and refill that will fix our pool water? If not, do you recommend that we gradually drain and replace the existing water with fresh? Should I bite the bullet and drain the whole thing and start from scratch?

I am concerned about potential "pool popping" as there is a lot of clay in our soil; we have a 6' fence around the pool and one of the fence posts "popped" last year and I don't want to risk having the same happen to an empty pool. Pool trucks in our area can deliver a max of 6,000 gallons at one time; would a drain and refill of 1 truckload every couple of days be a good way to gradually add the water if we don't go for a complete drain and refill?

Also, should I try adding lots of liquid chlorine (generic store bleach) to the pool at this point to try and get the CYA and the chlorine lined up to hopefully kill off some of the algae?

Please let me know if any additional info is needed and thanks in advance for your advice!

Nitrates are algae food and the only way to get rid of them is by replacing water. Your test readings are suspect, btw. There is NO pool water testing that has a precision of 2 decimal places and I suspect that yours was done with test strips in a reader, correct?
Assuming that your CYA IS above 100 ppm (which is probably is if you have been using dichlor and trichlor exclusively) yo need to use bleach or liquid chlorine to get your FC above 25 ppm (and it probably needs to be closer to 100 ppm). In a 36000 gallon pool this would be about 15 gallons (or 19 96 oz jugs) of 6% laundry bleach so if 12.5% pool chlorine in refillable carboys is sold in your area it will probably be a more economical solution. The carboys are normally either 2.5 or 5 gallons and I would suggest 3 of the 2.5 gal size ( or 1 and a half of the fivers).

It's much easier to answer your questions, when we know something about your pool. We often 'waste' the first few posts back and forth collecting information. So, please complete our new Pool Chart form -- it takes about 30 seconds, but will save much more than that.

Pool Chart Entry Form
Pool Chart Results

A few more things:

+ Get a cheap OTO (yellow drops) / phenol test kit, or if available at YOUR Walmart (check availability), get the HTH 6-way DROPS test kit, which is compatible with the Taylor K2006. Test the pool as soon and you can, and post the results. If you get the 6-way kit, ALSO test the water you FILL the pool with, especially if it's a well, and post THOSE results as well. (The HTH is the best available kit you're likely to find locally, but it's not the K-2006. It can only provide rough measurements chlorine levels above 5 ppm, and it measures "TOTAL" hardness, rather than "CALCIUM" hardness, which is not ideal.)


+ Having a good test kit makes pool care easier for EVERYONE. A good test kit means a kit that can test chlorine from 0 - 25 ppm, pH, alkalinity, calcium hardness, and stabilizer with reasonable accuracy. Test strips (AKA 'guess-strips' ) do NOT meet this standard. Some pool store testing is accurate; most is not. The ONLY way you'll know whether your pool store is accurate or bogus, is by testing accurately your own self. On the other hand, pool store 'computer' dosing recommendations are NEVER trustworthy -- ignore them. They are designed to sell more chemicals than you need, and WILL cause many pool problems.


+ We recommend the Taylor K-2006 test kit, which meets the requirements above, for many reasons. The HTH 6-way drops kit is a great starter kit, and is compatible with the K2006 (it's made by Taylor). There are a few alternatives; for example Lamotte makes an FAS-DPD kit that's OK -- but it costs 3x as much. But, we're not aware of any test that is better, and since we are all familiar with the K-2006 (and can help you with it) we recommend it exclusively ( Test kit info page )

Welcome to the forum! We are glad to have you here!

I typed a very long response to this thread about 1/2 hour ago, but when I tried to post, I got a message saying that the forum wasn't accepting new posts. So...I emailed it to Ben, but it's not here yet. Later this evening, when I can get back to the computer I was on at the time, I'll try again.

_________________________________________
OK, here it is...

What testing method did you use to come up with your test results? We very highly recommend drop-based testing here, because it is much more accurate than strips or computers are. Do yourself a favor and take a look at the K-2006 test kit in the link in my sig--it's going to be required if you're going to manage this pool with your CYA level that high.

You can fix the pool water in two ways...first, you can drain/refill part of your water to lower that CYA, or you can simply run a high CYA/high chlorine pool (which would be my pick of the two). Take a look at the "best guess chlorine chart" in my sig for a better explanation, but basically because your CYA is so high (due to the dichlor/trichlor use), you have to maintain higher chlorine levels to compensate. In your case, with a CYA of 160-ish (are you sure that's right?) you need to shock the pool up to a chlorine level of 25 ppm and hold it there, brushing daily and cleaning the cartridge as your pressure indicates, until the pool clears. It will become blue/cloudy at first, and then you can finish filtering out the dead algae After all the algae is gone, then you just have to maintain your chlorine levels between 8-15 ppm and you shouldn't have any further problems. (At this point, I'd switch to bleach, liquid chlorine, or a SWCG, though--if you keep using the dichlor or trichlor, that CYA is just going to skyrocket to the point where draining/refilling isn't an option).

I run a higher CYA pool than most folks around here--80-90 ppm, sometimes higher--and I like it that way. I don't have to dose everyday, and there are zero complaints from the swimmers I have about the water quality,.

Thanks much to the folks who have responded to this thread!

A local pool store is where I have obtained the results I posted in my initial message; I believe they use a computerized tester. My wife stopped by the store today to get the water tested and gave me the results over the phone; I'm home now and everything I posted above matches the printout.

On my way home from work, I picked up six 96oz jugs of 6% bleach. I brushed the pool when I got home, changed out the cartridges, lowered the water level a couple of inches and refilled with tap water from our well. I then poured all of the bleach into the pool; I will get more bleach in the pool starting tomorrow. (Hopefully it is okay to not add all of the bleach at once.)

I will get the pool water re-tested tomorrow morning on my way to work and will post a follow-up message here ASAP. I will also get a sample of the well-water tested. My wife will stop by our local Walmart and get the recommended testing kit... I'm not chemically savvy, so hopefully it's simple to use!

I have added my pool info into the pool chart as per Waterbear's request. (I was way off on the HP of our pump in my initial post! )

Thanks again for the quick replies; you have given me some hope that my "swamp" might actually become useable again! :)

If my math is correct, 6 96 oz containers of bleach = 4.5 gallons, which will raise the FC in a 36K gallon pool by 7.5 ppm, which is not nearly enough to clear up an algae bloom. Each gallon of 6% bleach in a pool that size will raise your FC by 1.7 ppm, and with your high CYA you need to get it up to (and keep it at) 25 ppm.However, you need to take a look at your well water analysis before you do this, because if you have metals in the water, then raise the chlorine that high, you may end up with a tea colored pool. So post your metals analysis here before you shock the pool!

The hth kit is not hard to use, but you'll have to force the chlorine test to read higher than it's supposed to by diluting your sample and multiplying (see this thread http://www.poolsolutions.com/gd/how-...d-testkit.html). That's why you need the K-2006--it will accurately test chlorine levels to at least 50 ppm without guessing.

As I said in my post you will need 19 96 oz jugs of 6% bleach!

Quote:

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Originally Posted by capshockeyfan

(Hopefully it is okay to not add all of the bleach at once.)

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Nope, Won't do the job. It ALL has to be added at once, the water retested, and more added as it is consumed to maintain the chlorine level at 25 ppm or greater.
A Taylor K-2006 will make things much easier for your. The kits from Walmart are just an inexpensive stopgap measure unti you get a good kit which will have to be ordered on the internet most likely.

I stopped by our local pool shop this morning on my way to work and they tested samples of our pool water and well water for nitrates. They are using a computerized system and it only gives out readings on nitrates up to 80, which is where our pool water is at... so at this time, I do not know how high our nitrates actually are, just that they are at least 80.

The good news is that our well water was clear of nitrates, so the new water I can add is not making the problem worse.

Aylad - Unfortunately, I did not see your post until I got to work, so I did not have the well water tested for metals yet; I will do so tomorrow. Just to confirm, the metals you are referring to are the iron and copper that the pool shop included in the test yesterday? (Are there any other metals I need to have tested for?)

The pool shop folks said it was useless to add chemicals to the pool until the nitrates were lower and the only thing I can do is replace the water. They were really busy and did not have time to run a full water test; their thought was that if the nitrates are through the roof, it does not really matter what the other results were.

My wife is picking up one of the Walmart pool water testing kits today and I will post those results here tomorrow; I will also order one of the Taylor K-2006 kits you are recommending. Given that it will take a few days for that kit to arrive; I'm hoping I can make some progress on the pool situation while waiting for the better kit.

I have thought about possibly running a high CYA/chlorine pool; before I make that call, can you tell me if people with sensitive skin might have a reaction to this type of water?

Waterbear - Sorry I screwed up with only adding a partial amount of the bleach; my plan was to add the full amount over the weekend when I have more time to devote to the pool. I thought it would be okay to pick up a portion of the bleach on my way home from work last night to get things started and then add the rest over the weekend. Lesson learned!

Given that my pool has very high CYA and nitrates, it is looking like at least a partial drain and replace will have to be done. If so, do you folks feel it is best to just drain the whole pool and start over with trucked in water; or would a gradual drain and replacement (6,000 gallons at a time) be a better way to go?

If we go with a gradual refill, my thought was to try and kill two birds with one stone if possible... get the chlorine levels up high right now to kill the algae bloom; I can then vacuum out the dead algae when I lower the pool water in preparation for the arrival of the trucked-in water. If I go this route, at least my pool will be free of algae once we have the nitrates and CYA in check.

I would stop worrying about the nitrates. If you kill the algae in the pool, then the nitrates don't matter. If you want to drain/refill part of the water, then I would drain/refill before killing the algae so that you're not wasting all the chlorine to kill the algae, then draining that nice, clean water out of the pool. However, I still think you could just stop using stabilized chlorine and run a higher Cl pool,, especially if you want to get swimming during this season. Folks with sensitive skin shouldn't have any problem with this type of water--a pool with a CYA of 160 and Cl of 10 is no more irritating to the skin than a CYa of 30 and Cl of 5. The chloramines are normally what will irritate the skin, but if you keep your chlorine at the appropriate level, you shouldn't have those anyway.

It's your pool and you are the one to ultimately make the decision. However, I want to caution you that completely draining the pool, if you have a high water table, can cause the pool to literally float out of the ground. If you decide to go that route, I'd make sure you have some professionals to help do the job.

I was reading your thread and although I am not knowledgeable enough to offer any insight directly to help with your problem, it did raise a question in my mind, and I hope I am not wrong in asking it here. Capshockeyfan has a problem with CYA levels being very high. I understand that you can maintain high levels of CYA as long as the chlorine levels are in somewhat of a proportionally high level. My question is this; Does CYA ever break down or go away through its normal chemical process or reaction with chlorine? Is it ever consumed? If so, how long does it take for CYA to break down and what chemicals does it break down into?