Adjusting chemistry with 100% water replacement

Our private swim club has a 100% new water this spring. We have a ~55,000 gal in-ground pool w/ a NEW vinyl liner (thus the water replacement last fall). The pool was built in 1964. The pool was shocked last fall before closing -- I don't remember the chlorine level. The club (a co-op) will be opening the pool this weekend to prepare for Memorial Day swimming. We must pass township inspections for chemistry (chlorine, coliforms, electrical, etc.) the week prior. I am the CPO (Certified Pool Operator) and have taken the course on-line to become a CPO and I am a chemical engineer by training so chemistry isn't new to me. I was the CPO last year but things were pretty much "normal" and I got tips from the former CPO. With the water replacement and not having a commercial company doing the opening, I am sweating getting the chemistry right for swimming and thus opening. We have a DE filter w/ an erosion feeder and we are using tri-chlor tabs. We have a full Taylor DPD test kit (which I am familiar with) except the tube to read CYA (don't ask me where it went and I'm not sure I can replace just the tube - suggestions). All testing chems were stored in my basement for the winter. We don't have a high bather load (many times we are the only family there). Membership is restricted to 40 families.

How do I start this process? I am planning to pull a sample of the water from under the cover tomorrow or at latest Saturday AM and test it myself and also take to pool store for testing. I will also inventory chemicals. I have shock, tri-chlor tabs, and baking soda (I think) in hand from last year. Typically we have consumed a fair amount of baking soda (low pH - 6.8 -7.0 range) and last year chlorine ran high all season. The pool rarely if ever has used sodium hypochlorite although we have it in the chem shed. I doubt there is any CYA in the pool b/c of the refill. I had the supply water tested (well) before filling last year and iron and copper are fine (low).

Should I shock before addressing the pH? What level should I shock to? During the season we shock once a week at a set amount (member family does each Sunday night b/c bather load is low on Mondays). After shock and pH, address CYA? What if there is a lot of algae (have had both black and green algae in the past).

We have a large crew on Saturday to pull the cover (25' x 50'), reassemble pump (new last year -- anti-suction and very touchy to air), clean and reassemble filter, in addition to a myriad of other tasks. Vacuuming will be done 2-3 times a week until guards start at the end of June. A log of any chemistry adjustments (or changes to the erosion feeder) is kept at the pool. Because of the timing of opening (two weeks), I would like to have what I need on-hand to eliminate trips to buy chemicals (or the grocery/Sams Club for baking soda). I'll be running to the pool enough. The pump will probably get started up late Saturday or early Sunday depending on how long it takes to get the water level up.

I am new to this forum but I learned a lot of practical advice from it last year and this is my first post.

Thanks in advance!

Hi CPO;

I think I'm the only one regularly on the forum with much experience operating commercial pools successfully, so I'd better take lead on the responses.

I'm assuming that you've peeked under the cover, and that the water is still clear?

If so, I'd use bleach or dichlor to add at least 10 ppm of chlorine BEFORE you remove the cover. Pools that have wintered without circulation can have an active population of of bacteria and more when opened, and can turn green in hours!

Bleach would be safest, for your liner. But, bleach typically doesn't keep well. Bleach stored since last year might be 1 - 2% chlorine. Clorox brand household bleach stored cool might do better since they filter for metals, which catalyze decomposition. But take a look before you use it. If it's discolored, flush it, a gallon at a time, till gone.

If you use dichlor, dissolve it first. (Wear old clothes and shoes, along with glasses, when you do!)

Get a new K2006C, ASAP. You WILL need to know CYA levels!

Get a copy of your local pool code, and learn it. Go over your last few inspections to find out what your inspectors focus on. Find our what the allowed pH range is, and the maximum chlorine level. THEN find out what sort of violation HIGH chlorine is. In this state, pH violations, and HIGH chlorine are "2 point" violations, meaning points off but no re-inspection and no enforcement action. This is critical for me, since I normally run pools at higher than code chlorine levels. Also find out what allowed CYA levels are, and what kind of violation it is. For a commercial pool without an onsite operator, high CYA + high chlorine can allow 1x per day dosing . . . if the violations are just 2 point violations.

Do NOT use baking soda to raise or maintain pH -- use borax. As it accumulates, it will help with the algae. But you'll get some strange looks the first time you leave Walmart with 25 boxes of borax!

You asked what levels to shock to? With no CYA, I'd limit my first shock to 10 ppm. After than, the answer I'd give depends on your codes and what you're comfortable with. I shock to 10 - 15 ppm in the evening, with CYA levels > 60 ppm, so when the swim team is in the following AM they may be in 10 ppm water.

You'll need to have enough bleach or dichlor on hand to shock to 10 ppm nightly till you get CYA in the water. And, you can't really add CYA till your pool is clean enough so your DE filter can run 3 days without cleaning. Once that happens, add your CYA carefully to the skimmer, so it can dissolve out on the filter.

Find out where your feeder is in the pool circulation loop. If it's downstream of your filter, that's good, since that will allow you to add chems to the skimmers, and not have to worry about the effects of undissolved chemicals reaching the feeder.

. . . . that's probably enough for now.

Ben

Checked the chemistry tonight.

pH 7.0
Chlorine -- 0
TA 90
Ca 260

The water is clear. Some scum/algae at water line (at corner that cover has cut straps). The chlorinator is after the DE filter. I missed the pool store but I have a fair amount of shock (calcium hypochlorite), some pucks (tri-chlor), soda ash and baking soda. The water level is below the skimmers so I can't start the pump until water is added (pump is very touchy w/ air). It will take 4-5 hours to add enough water. I'll see how long I can hold off on pulling the cover tomorrow while we are working on the filter. It is supposed to be cloudy and rainy. The pump is disconnected from the filter.

I'll prepare to shock as soon as we get the pump running.

cpopisc -- Just wanted to welcome you to the forum and also to thank you for becoming a subscriber. We appreciate the financial support in keeping the website alive.

Question for Ben --- even if his bleach has lost its potency, couldn't he just go ahead and add it to the pool rather than flush it? My thinking is that it would add maybe a little chlorine and it wouldn't hurt anything and it would get rid of it. Correct me if I am wrong.

It should be brine, which shouldn't hurt. It can still be tested for potency. Somewhere around here I have have the "recipe". I think it's 10 ml added to 10 liters of un-chlorinated water (5 soda bottles) gives you the same dilution as adding 1 gallon of the stuff to 10,000 gallons of water. Then you can measure the FC level in the 10 liters and it will give you the concentration...3ppm means 3%.

Carl