Can anyone provide any guidance or pointers please - we are repeatedly isolating pseudomonas from the routine sampling and despite shock dosing, filter sand change, backwashing, shock dosing and more shock dosing the problem recurs.

Bilbo

have a little experience with pseudomonas problems in spa pools. What are you shock dosing with? Is it just the standard disinfectant you use (usually Chlorine of Bromine) but just higher levels, I've seen that tried and does not often do the job. Usually need a specific bio film cleaner of some description to get to the route of the problem.

Hope that helps

Thanks for your offerings folks - just to clarify this is a hydrotherapy pool not a spa; filter sand change was due anyway; pool emptied and cleaned, refilled woith fresh water, WHOLE system shock dosed with usual disinfectant, including incoming supply pipework. balance tanks, filter tanks - system run through six cycles pH balanced and disinfectant level corrected. Weekly microbiology tests clear for 3 consecutive weeks - then a positive for pseudomonas.

Still open to further advice.

Thanks canopener - I too am clutching at straws - willing to try anything as the pool has now been closed for 2 months. I would add that the pool entry is protected with an "airlock" any outdoor shoes are not permitted past this point. The poolside is cleaned daily using pool water, there is pre and post bathing showering regime in place and is rigidly enforced. Routine daily pool water tests indicate disinfection rate and pH is fine. There is something I am missing somewhere - I just can't put my finger on it! Thanks again to all.

I'd like to back-up one of the previous comments.

Pseudomonas is infamous for surviving within a biofilm. Shock-dose as much as you like but it probably won't finish off an established biofilm within the pipework or some valve/surface within the system. You should double-check whether an appropriate bio-dispersant is being used as part of the specific cleaning process in addition to your disinfectant. It wouldn't be normal to have it regularly dosed but would seem valid in this instance - re-occuring positive samples after a fallow period screams of bio-film to me.

Chlorine/bromine are wonderful at attacking the bacterial cells they can get to in 'open' water. Biofilms partly exist to protect the bacteria and the halogen compounds are not penetrative, certainly not to the point of finishing off a decent biofilm. A good bio-dispersant should 'lift' them off the surface they're on though and make them available for the oxidising biocide to attack.

Bilbo
Apologies if I have misunderstood what is happening and if you have done this already;
As I understand it, what you have been doing is cleaning the pool and the associated equipment, and then testing the pool water to see if you are getting a Pseudomonas count. Have you tried to take swabs from the areas where you thing the contaminant is coming from eg the pipework etc? That way you can close in on the suspected area and eliminate the OK areas.
Have you checked the water supply for contamination?
Are you actually culturing the samples are you relying on a test kit?
If it’s test kit there could be a problem with false positives.
You need to talk to a environmental microbiologist.