ORP - Have I messed up?

ianhutch1 · Jul 11, 2016

Hi all have been lurking for a few months and need some advice please

I am in Australia and had a new fibreglass pool installed in March. It has a AstralPool EQ25 control system (http://www.astralpool.com.au/sites/default/files/products/manuals/INST%20315%20EQ%20CHLORINATOR.pdf) which controls PH and ORP with a SWG and automatic acid feed.

I've invested in a Taylor K-2006C test kit which is excellent and have spent the last month or so getting all my levels balanced in accordance with the TFC guidelines, so far so good! Going off the suggestions for SWG pools I got the CYA levels up to 80 and FC using the test kit to get to around 6 to compensate.

Now my main issue to that the control system is going haywire with ORP fluctuating wildly (700+ readings in the mornings and 580 ish at around 5pm) and the SWG is pumping out loads of chlorine when I don't think its actually needed and its eating through acid at a crazy rate all of a sudden. After re-reading the manual (I know, I know..) it appears that a CYA level of 80 is way too high to be using with this type of system and they recommend not using it at all or at most having a range of 10-20ppm.

What options do I have now to sort things out? Am I looking at a pretty much total drain and refill of the pool (water is expensive here) to use this system or am I best to switch the system off and manually balance the pool for the summer season (its the middle of winter here now) then see how it looks at the end of summer?

I paid a lot of money for the system with the pool so not using it isn't ideal but I think I'm right in saying that there is no easy way to bring the CYA level down so the system works correctly?

tim5055 · Jul 11, 2016

Welcome to TFP!

I think the bigger problem is that ORP is really not consistent long term. It is one of those things that look good on paper but doesn't seem to wood well in practice. From what I have read from other users is that the probes need regular cleaning and replacement for any hope of consistent readings.

Now, to your specific question - the only way to reduce CYA is through water replacement.

ianhutch1 · Jul 11, 2016

Thanks for the welcome and quick response and yes the probes have to be cleaned every 6 months, I think my best course of action is to reduce the ORP value down on the controller to stop it kicking out chlorine and just monitor it manually for the next few months running the SWG manually as required. I'm hoping I can find a value on the controller which works for the amount of CYA in the pool and if it continues to go mental consider a drain then.

Great forum by the way I'm learning a lot

ianhutch1 · Jul 11, 2016

Sorry one more question. I have noticed that the ORP value on the controller goes down rapidly as the SWG is in use, is that normal? I would think that ORP would increase as chlorine is added?

Bama Rambler · Jul 11, 2016

The issue, as you have surmised, is the CYA level you have. It interferes with the ORP reading, and not in a linear way.

You are right about running the system in manual on time and percentage until you can get the CYA down to a manageable level. I'd say it needs to be 20 ppm or less.

JoyfulNoise · Jul 11, 2016

TFP guidelines for SWG pools are not written with ORP in mind. For an ORP system, you use only a very small fraction of CYA, 30ppm or less in most cases. This allows the signal (hypochlorous acid) to noise (everything else) ratio to be high enough for the ORP system to achieve stable readings.

The downside is, with such low CYA, your FC will be constantly destroyed by the sun and so the ORP system will be running your SWG constantly to maintain the overall lower FC level (2-4ppm FC). TFP recommends higher CYA levels (and higher baseline FC levels) with an SWG because it actually allows the SWGs to be run less. Higher CYA results is lower daily FC losses.

So that is the price you will pay - you can have automated FC levels BUT you will pay for it by having having to replace your SWG cell more frequently, your ORP probes will need regular replacement and you will use more acid because of the heavier SWG use.

ianhutch1 · Jul 11, 2016

So it sounds like I may as well just turn the ORP probe off and run the SWG on a percentage basis as thats what is going to cost me less in the long run. Wish I had read this site before making the investment! Thanks.