I had a feeling I would be reprimanded for my misdemeanour.
The 'algaecide' (hate that term) was a 40% polyquat; I made sure of that and wouldn't have used any other type.
http://www.poollife.com/index.php?optio ... &Itemid=57
Don't misunderstand me, I'm not at all knocking the 'sustained-shock' BBB approach. The pool was steadily clearing (down to a moderate-light white haze after 5 days), but it wasn't going to happen overnight and there was pressure to get the pool up and sparkling for the weekend.
I did consider using the 'Clarifier' (the bright blue stuff- polyacrilamide ?) left over from a pool opening kit (HTH) that I mentioned had been given by the previous pool owner, but it was probably at least 2 years old and, and I had read that if not used properly they can make matters worse, - didn't want to take that risk.
I had used the same algaecide last season when I had a mid-summer green algal bloom. I remember it well. Shocked the pool, it turned white, but still hazy after 24 hours. Whats wrong? Water sample to the pool store for analysis. The diagnosis - algae (really, there's a test for that?). You'll need this - Zap-It. I know it's algae, but surely it's dead....it's turned white. Never mind, take our advice, or it will come back. So how much do I add? The whole bottle, yes all of it, shock again after two hours, keep the pump running overnight, back-wash in the morning and again the next day, vacuum and you are done. Next patient please. Well it worked - by the next morning the pool was clear with the dead algae settled on the bottom.
But within a week it came back - despite adding the prescribed weekly 'maintenance dose' of algaecide. Inadequately controlled chlorination maybe played a part (just had a puck in the skimmer), but the main locus seemed to be a bath mat (natural rubber as it turned out) I had put under the pool steps to protect the liner. The under-side was clear, but the surface of the mat inside the steps was heaving. Took the mat out and algae cleared up. Cleaned the mat, put it back and the algae came back within a day or two. Tried adding the weekly algaecide behind the steps, but same result. And so it went on - removing the mat at the end of the day, cleaning it and putting it back before people swam. Very tedious and by the end of the season the mat had all but dissolved. This year I've found an all vinyl bath mat and will see if that works out better. If not, I might try using suction cup feet under the steps to improve the circulation. Either way, I hope that my intent to take better control of the water chemistry will make a difference.
So, no, I don't really have much faith in the algaestatic, let alone algaecidal properties of these poly-quat products, at least at the concentrations used in domestic pools, and I think the notion that somehow increasing the concentrate from 15% to 60% changes the chemical from a mere inhibitor to a ferocious destroyer, mercilessly lysing algae cell walls and spilling their contents (as some articles and product promos portray) is, to say the least, exaggerated:
http://www.clubpiscine.ca/78-tips-and-a ... uctor.html
http://rob-dr-duck-coxworth.wrytestuff. ... 113446.htm
Quote:
"Algaecides are chemicals that kill algae as opposed to sanitizers like chlorine that prevent algae and bacteria from getting a foothold in the first place".
Even the product I used, quote:
"A weekly dose of Zap-it will kill all algae present in the water and protect against any future growth."
Not my experience.
I do think however that they (at least the one I used) are quite effective for flocculating chlorine-killed algae, probably acting in much the same way as the other polymeric chelating agents used in the clarifying products - cross-linking/binding cells together until they floc.
Whether those products are more effective or rapid, I don't. But on this occasion again, after adding the 150ml of 40% poly-quat early evening (pool maintained at shock level), the filter pressure was up within a few hours. Back-washed at mid-night. By next morning the water was very clear, with lots of settled algae on the bottom. Back-washed again and dosed up the chlorine. Late afternoon after work, vacuumed and then ran for a few hours on bottom drain only. Had been a hot day and FC had dropped to around 5ppm (strip test) by this time. Dosed again to shock level and switched back to mixed skimmer/drain. Next morning there was just a little dead algae to vacuum. Let the FC fall to 5ppm again and have kept it there. Don't yet have the Taylor kit so couldn't do a proper overnight loss and combined chlorine test. On the strip test, pH (7.2) and alkalinity (80) look OK'ish. The CYA is just registering in the 35-50ppm range. Only used Ca-hypo for the first shock. But I should probably take a sample in for full testing.
I promise not to do it again. Now, am I still on probation, or do I have to wait for the Taylor kit?
Irony is the weekend has been a washout with no sun expected until Tuesday.