Weird...... Spa attached to pool issue....


LifeTime Supporter
Jun 23, 2009
Here are my numbers:

FC = 7
CC = 0
TC = 7
pH = 7.6
CH = 310
TA = 90
CYA = 80
Salt = 3200

My pool has a built-in spa that is attached to the pool and the water flows from it into the pool and there are also 4 returns in the pool itself. All the returns are on and water is flowing everywhere it should. I did an overnight test this past weekend, no CC and no FC loss. It's been really hot here and I just wanted to make sure everything was on the up and up.

Here's the weird part, today when I got home, did my daily FC and pH test and as I walked by the spa, I found a couple small patches of what looks like yellow/brown algae in the spa where the bench meets the wall. I tested the spa and had the same results as the pool sample a couple minutes earlier. I guess I will do another overnight FC test this weekend, but it just seems weird that it shows up in spa and not the pool and I have not let the FC go below 6 the last couple weeks...



TFP Expert
LifeTime Supporter
Mar 29, 2007
Coastalish 'down easter'
If it's only thoughts you want, I'll go ahead and speak up :)

Which way do the directional inlets in the spa point (do a couple point down to stir up the bottom of the spa)? There may be areas of low water exchange that aren't 'seeing' the chlorine you have in the water.

It's a shallower and, thereby warmer body of water and therefore may have a higher chlorine demand than the pool.

Are you testing the water from ~ 18" down?

Are you sure it's not just dirt? :lol:


TFP Expert
May 20, 2007
South Central NJ
If the spa is getting significant on time during the day and you have an automation system, the automation system usually reduces the cell output to 2%. Poof, there goes the FC if it's on for more than an hour.



TFP Expert
LifeTime Supporter
Jan 6, 2010
San Dimas, CA (LA County)
Thoughts... :rubbing chin and looking thoughtful:

Dead zone in the spa? I have the same setup as you, and through experimentation, I found a setting on the three way valve that draws just a little water from the spa, the majority from the pool. Then I set the return so that I just overcome the draining from the spa, so there's a trickle going from spa to pool.

The corners tend to be poor circulation areaS in the spa. The back edge of the seat and the edge of the floor are where I find little bits of grit settled out.

Whether it's dirt or algae, I'd say you need to brush more. Not what you wanted to hear, I'm sure.


LifeTime Supporter
Jun 23, 2009
Thanks for the input all...

I'll look at the circulation when I get home. (Richard it's very similar to yours and I occasionally change only if i need to aerate) I think I have a new chore for my 13 year old this summer....LOL

Update: I isolated and shocked the spa after brushing yesterday. When I got home, clean and not a sign of algae.
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