Slam or not to slam?

[PeterDM]

Politely requested not to add my post to another thread ... so here's a new thread.

I've owned & maintained a 12' x 24' x 5' inground vinyl pool (about 40,000 kiters) for 7 years. In southern Ontario - so a short 3 month season. Varying degrees of success in keeping the pool trouble free over the years, but frankly, haven't had a clear idea of what I've been doing. My wife ("just stick other puck in") hasn't been much help!

This year I rapidly cleared up green water after opening, but then green water started coming back. Shocked it a couple of times & gradually got it back to more or less clear. After a couple more weeks the pool started going cloudy & a bit green again. Since then I have been battling very day to maintain water clarity. I have NEVER used liquid chlorine - only HTH powder in conjunction (sometimes) with pucks. After coming to this site, I have started using liquid chlorine only.

The situation right now: I'm waiting for my testing kit to arrive (should have it on Tuesday). In the meantime I have been adding 1 - 2 liters of liquid chlorine to the pool each night. This has resulted in clear water but always some precipitation of algae at the bottom of the pool ... not a lot, but a light haze of green. My test strips indicate that the chlorine level is between 5 &b 10 after adding the chlorine in the evening & around 5 the following morning. The CYA levels? Hard to say. According to the test strips somewhere above the "ideal" level, but below the 100 level. The last reading from the pool store was 63, FWIW. When I vacuum the pool each morning I do it to "waste", which lowers the water level by a couple of inches, which presumably, is helping gradually lower the CYA level.

Obviously, I need my testing kit to proceed further, but assuming the chemistry is more or less where I think it is, the question I would have is this:

if the pool water is basically clear, but there is some algae precipitation on the bottom of the pool each morning, is it reasonable to continue with appropriate maintenance levels of chlorine in the expectation of gradually eliminating the remaining traces of algae, or is a SLAM required to kill it off completely?

Thank you!

 

[Davejavu]

Getting the right test kit is necessary before good advice can be given. Accurate CYA will help determine your issues and give you the right FC to maintain. But yes, if it was green, then a proper SLAM is in order.

 

[AimeeH]

Hi and welcome to TFP. I'm going to suggest you will need to SLAM as I've found from my own experience that not following through the whole process that there is algae hiding in waiting that will return very quickly, which sounds like what you are seeing.

Once you get your test kit that will help you determine for sure by testing for CC and being able to do an overnight free chlorine loss test (OCLT).

 

[PeterDM]

Here are some photos showing the current state of the pool. The last one, with enhanced contrast shows the algae on the bottom.

It sounds like a more aggressive treatment is required. It's interesting because in past years I haven't really encountered recurring algae like this ... but who knows what the chemical balance really was at that time.

 

[AimeeH]

Oh yes. SLAM is in order. Looks like you have algae.......alive, not dead.

 

[PeterDM]

I don't think there's any question that there's "living " algae, because I vacuum it & it reappears over night, albeit in modest amounts. What I wasn't really clear about was whether a consistent regime of correct FC levels would get on top of this, or if a SLAM is absolutely required. It sounds like a SLAM is necessary.

 

[Davejavu]

What I wasn't really clear about was whether a consistent regime of correct FC levels would get on top of this, or if a SLAM is absolutely required. It sounds like a SLAM is necessary.

The SLAM will eliminate ALL algae. Once gone, maintaining your minimum FC and other numbers will keep it away FOREVER.

 

[AimeeH]

I don't think there's any question that there's "living " algae, because I vacuum it & it reappears over night, albeit in modest amounts. What I wasn't really clear about was whether a consistent regime of correct FC levels would get on top of this, or if a SLAM is absolutely required. It sounds like a SLAM is necessary.

You are correct that SLAM is in order. The reccomended chlorine levels for SLAM are intended to kill the algae faster than it can reproduce and maintaining that high chlorine level until you pass all three tests.

Clear (no algae) water
Cc of less than .5
OCLT loss of less than 1

Just slightly elevating chlorine and brushing in hopes of ridding the algae will likely leave you spinning your wheels and continuing what will be a losing battle. Ask me how I know

 

[Divin Dave]

Yeah, SLAM it.
you wont be able to slowly eradicate the algae by regular FC maintenence levels. The lower amount of FC will be quickly used up in killing the algae. Its important to MAINTAIN a shock FC level until the algae is done and gone.

Judging by the looks of your pool, it wont take you long at all to SLAM it and be in good shape.
Remember that when you slam, you need to brush the walls and disrupt the protective "slime" coating on the algae so you can get that pest exposed properly to the chlorine.

 

[PeterDM]

Got it! A slam it is!