My pool has gas?? - Mystery solved??

[zinengineer]

Just completed conversion from Baquagoo Mark's conversion and I'm in the process of getting the chemistry lined up. Wasn't sure to post here or in "chemistry", but what the heck

latest set of numbers

FC = 2.5 CC = 2.5 (I know this is a little high but I'm adding bleach each night to bring up to ~10FC)
CYA ~40 (I added some this weekend and will wait to test, this is a calculated number)
TA = 170-180 (depends on how I count) CH = 270
pH = 7.5

So I'm working on getting the TA down. Towards the end of the conversion the pH was holding around 7.2, so I decided to areate for a while to see if I could start getting the TA down. I ran the waterfall pump and air to the spa for about 2 hours last night.

Tested again tonite, the pH drifted up from 7.2 to 7.5 and it looks like TA is holding - not surprising as I assume I'll need more areation.

My question - after I turned off the air and left the filter pump circulating all night and today - I'm still getting gassing at 3 of my 6 spa returns. The spa and pool share the same filter pump, and I'm not seeing the gassing in the pool. I'm guessing there is a fair amount of dissolved oxygen and CO2 which is gassing at the spa jets since they probably have a bigger pressure drop (smaller orifice?) than the pool returns.

Is it normal to have a pool with gas?

 

[JasonLion]

Spa jets are often venturi jets, which means they only need water flow to pull air in and bubble. It sounds like you have a blower in addition to venturi jets. Between the blower and the venturi jets you get the maximum amount of air possible, but the jets alone will still get some air.

With CYA at 40 you should be bringing FC up to 15 to get rid of CC. FC at 10 will work eventually, but 15 should go noticeably faster.

 

[Guest]

Many spas have air control valves, often 2 of them, to allow to you inject air into 1/2 of the jets at a time. If you have them ( usually mounted on the top of the spa) then one of them is probably open.

 

[zinengineer]

So, I think I've figured out the mystery.

When I areated with the spa blower, I simply turned it off and left the pump running overnight. Today, I let the pump timer turn off the pump per normal schedule.

Wife turns on pump before I get home so I can test in the evening.....no air bubbles.

My guess.....when the blower turned off it didn't completely "seat closed" and was leaking air into the spa return line.

I'll have to test this theory when next I use the spa.

8)

 

[vessmech]

I had the same situation - air in my spa jets without the blower on.

Turns out the blower is just set on the vertical pvc riser pipe - not glued. I assume this is so you can remove it for maintenace or replacement. With the pump running in "spa" circulation mode, you can put your hand on the riser pipe and feel the vacuum being pulled from the flowing water to the spa. So either air is leaking past this connection or air is leaking through the blower...I'm not sure if there is some sort of "check" valve on the blower to keep this from happening when it is not on.