Chlorine pool spikes?

[Stunnn]

HI All,

I have run a small hydropool for some years with it's various quirks. Recently I have been given eleven schools, all with various problems, however:
I have just inherited a team who have a 25m x 11m x (1-3m deep) pool which is 12+ years old.

There are many problems to sort in the schools, and I heard nothing about the pool, so have not looked at it.

Recently we have a couple of competition clubs complain of breathing problems, so investigated and the CL is ~5ppm. Closed the pool, let the CL drop, check the dosing, check the testing, logs all look good..

Re-open and all is well until the competition groups come in again.
I sat on the side, taking readings whilst they rip up and down the pool - the CL levels rise from 4 to 5 ppm

There is some black dust at the bottom of the pool, that is daily swept to the outlets.
I would normally run a pool at CL 2ppm, and close >1 or >4, with PH of 7.2-7.4 (Close <7 or >8) - this pool has been running at 5ppm for some time.

My thoughts are that during low use, there is chlorine build up with the crud and in the corners/depths of the pool.
When the clubs come in they stir it all up, bringing this extra Chlorine in.
Pool is currently closed as I scratch my head with this. We had dropped the pool CL to 3 and I have changed the setpoint to site 1.8-2.0 ppm.
I am also buying a pool hoover as soon as accounts get the account set up (Monday?).
MEanwhile recomending as much water turnover as possible.

Am I going down the right line in your experience?

Cheers,

Stu

[Teapot1]

Are you measuring free available chlorine or total chlorine which would include the chloramines?

[Stunnn]

Hi Teapot1,

Sorry, I should have said - Free Chlorine.

[Teapot1]

No problem, just thought I would ask.
When were the sensors cleaned or changed? In the past I have been called in to look at over dosing and the probes were 10+ years old, they are expensive so owners often over look them at service time.

[Stunnn]

There was a new doing system installed over the summer holidays (Certidos LDPHCL)
Part of the buildup (I think) is that before I started asking questions, the site team left the engineer to calibrate it on his monthly visits.. as they were not confident about using it... That has now changed, thankfully.

The piping, ect is 12+ years old though.

[Teapot1]

Ok and the filters, when were they last stripped and cleaned and what type? Sorry for all the questions

[Stunnn]

Hi Teapot1,

Questions are good.
Last service of the filters is unknown.
I think we can safely say that they need changing.

[Stunnn]

Forgot to add - They are sand filters (Which may be original 16 years old )

[Stunnn]

Just to update this post...

We reduced the setpoint "range" for chlorine to 1.8 - 2ppm (was previously at 5)

Pool hoover purchased (wave 100 pool cleaner), which doesn't hurt at all.

Many backwashes..

All seems to nw be fine (touch wood)..
Pool side surface chlorine readings are ~1.7 from normal use, plant side ~2ppm.. Under heavy use the Pool side rises to ~2ppm, so definatly a low level build up and the thrashing mixes everything (as you would expect)...
Hope this helps someone else in the future..