no problems right now, but curious

in addition to adding appropriate levels of Cl- would covering pool to block out sunlight help fight algae?
Algae is a plant, requiring light for photosynthesis, right?
Just thinking, if I get an algae bloom like I did last year while on vacation, would it be worth it to cover pool while away 2 weeks? or if not, would it help fight the algae?
Took me a month last year to fight off the algae- that's when I discovered this sight and found out the CYA screws around with the Cl, so I spent 2-3 weeks without enough Cl to do the job...

Some algae requires very little light. In my experience, if ANY light can get through, algae can thrive.

But even a completely opaque cover does nothing to stop bacteria or biofilm formation. So far as I can determine, the relationship between purely bacterial biofilms (under 100% opaque covers) and algae is not understood. But there is some sort of relationship. I've seen pools, that opened with crystal clear water, but slightly slimy (biofilmed) walls, turn dark green in less than 6 hours.

Keep in mind that a septic tank is a thriving bacterial hive, in total darkness. Having your pool resemble a septic tank is not a commonly held goal.

OTOH, if you shock your pool and get it crystal clear and algae and combined chlorine free (allow a week) in the days preceding your vacation, add extra chlorine and THEN cover it for 2 weeks, your chance of returning to a pristine pool is much increased. If you can get a friend or relative to drop by, and pour several gallons in after about a week, so much better.

But, you do not want to shock a dirty pool and immediately cover it with a solid cover, especially if the pH is below 7.8. The some of the chlorinated compounds that form as the "goo" is destroyed are volatile. These compounds will tend to accumulate and concentrate just under the cover, and can damage it. So get the pool pristine, wait (maintaining high chlorine) and THEN cover.

Of course, this is much less of an issue with a mesh cover . . . but mesh covers don't keep out all the sunlight, either.

Ben

Thanks for the input! I was just thinking, yesterday while dissolving salt for the pool, about things that might help...
Can't help but be curious, and ask!
Thanks again...

In addition to the steps Ben outlined for you above, I believe in the past he sometimes has also recommended using a dose of 60% Polyquat algaecide before going on vacation. Algaecides are not very good at helping to clean up an algae mess, but they are a pretty good preventative. (That is the only type of algaecide recommended.)

Thanks, Watermom.

One detail to keep in mind: you can't do BOTH high chlorine and polyquat. Or rather you can, but it's not real effective: high chlorine breaks polyquats down.

Ben

good to know about the polyquat/Cl incompatibility...
Thanks again!

It's not quite as bad as "incompatibility". This post has a response from Buckman Labs that make PolyQuat indicating that though chlorine breaks down PolyQuat into shorter chains, they are still effective biocides. I would read their recommended approach which is to shock first, then wait a few days and add PolyQuat. Though the remaining shock level of chlorine might break down some of the PolyQuat, that should still be OK.

What I think would be wasteful and be avoided would be adding PolyQuat and then shocking since the high chlorine level will mostly just break down the PolyQuat thus defeating the purpose of having an elevated chlorine level.