Newbie-Chemical Help

18000 gallon in ground with spa.

Delta UV system and nature 2 Mineral Pack. 3HP intelliflow with automation. Pentair 2hp whisperflow for waterfall. Pentair 520 membrane filter. Mastertemp 400000 heater.

Phosphates greater than 1000. just removed crepe myrtle due to amount of crap it was putting in the pool. Have 7 Chlorine tabs in chlorinator in wide open setting but getting zero chlorine with Taylor test kit. Will be treating phosphates next week.

TH 300
Chlorine 0
PH 7.2
TA 80
CYA 60


With my UV system and mineral pack FC under 1 PPM should be ok according to pool builder.

Biggest question - anyway to measure Chlorine levels less than 1 ppm with Taylor Test kit?

Hi and welcome!
You can measure FC down to 0.2ppm with the Taylor K-2006 or K-1515 FAS-DPD test. But why bother?

We've had HUGE discussions here about Ozonators (is your UV kit one of those) and almost universal disdain for Nature2. Your pump sounds insanely huge for your pool, and you need a really big filter to make it work well and not present problems.

TH=300 is normal
pH of 7.2 is the bottom of the normal range but if you have algae, that's fine (Chlorine is more effective at lower pH levels than higher ones).
TA is fine
CYA = 60 means you need to maintain your FC (free chlorine) between 5 and 10ppm unless you have an SWCG (Salt water chlorine generator), in which case you must keep FC over 5% of CYA--ie, 3ppm or greater. But you need to shock your pool right now up to 20ppm to kill that algae or your pool will never be clean.

You'll need to put in more than 4 1/2 jugs of 8.25% bleach (regular, unscented,in the 121oz jugs) just to get close to the 20ppm. You'll need to keep it there at 20ppm until the algae is good and dead. Each jug of bleach will add 4.33ppm of chlorine. You'll need to test 2x to 3x/day, vacuum and brush every day until it's clear.

Builder says it's OK. You have algae. We'd say it's not....

Hope this helps.

Thanks Carl. I forgot to say I don't have algae! Unless phosphates are considered algae? Water is actually beautiful.

My UV system is just a UV light. This technology does not create OZONE. Just alters DNA of bugs/algae so they cant reproduce.

In which case you are in maintenance mode and need to keep FC between 5 and 10. If the N2 is working for you, you can stay closer to 5. Phosphates are food for algae. If you don't have algae, the phosphates do nothing. Very few here ever need phosphate removers, and those few have persistent and tough mustard algae.
I have never heard of a UV light in a pool. If it can damage the repro cycle of algae and insects more than sun light it may well break down your chlorine faster. I do not know.....

DELTA UV is what I have. Small description of how it works-

E and ES Series both offer an incomparable and safer pool experience for your family and friends… Silky, smooth, odorless and salt free.

The water circulates through our Delta UV sanitizer that uses the type C ultraviolet rays to completely purify water deactivating all the dangerous micro-organisms resulting in the cleanest and purest water possible for your pool. As small residual of chemicals are used in order to destroy any micro-organism that do not find their way into the UV sanitizer.

I am going to check the plumbing arrangement to make sure Chlorinator is down stream of UV system.

I will ask Ben to look into it.