Swimming pool - auto Ph or auto chlorine

We’re in the process of converting our 50 000 litre pool from “fresh” water to “salt” water. We’re not very good at maintenance, so we want to automate as much of the process as possible - this is one of the reasons we’re going to salt. To have chlorine automatically generated will save time and money.

The chlorinator we’re looking at is self cleaning (by reversing the polarity of the plates, I believe), and costs around $AUD1250. We’ve seen devices that have a probe in the water to determine the chlorine concentration, and adjust the output of the chlorinator accordingly. One of these will cost us around another $AUD1000.

The Pool Shop Guy thinks that we don’t need this: once you get the chlorine setting right for your pool, it stays pretty stable, he says. What we do need, he thinks, is an automatic Ph tester. This device (which costs around $AUD850) also has a probe in the water, and will add muriatic (hydrochloric) acid from a drum as required to lower the Ph of the pool (chlorine pools tend toward alkalinity).

Our pool is old, and the Ph seems to remain fairly stable - I’ve never added acid in the four years I’ve been here (but I haven’t tested the Ph very often either). Apparently keeping the Ph in the right area makes the chlorine more efficient at sanitising, and prevents corrosion of pool surfaces, particularly in an old pool such as ours.

We intend to resurface the pool in the next 18 months or so. The current surface is around 30 years old, and all chemically active stuff has leached out long ago, so it doesn’t seem to affect the water quality. A new surface will probably have a significant effect on the water quality for several years.

So, do we go with the chlorine sensor or the Ph sensor? The Pool Shop Guy just happens to have a Ph sensor in the shop, but would have to order a chlorine sensor (even though he would make a bigger sale). He also advises that no-one makes a device that does both jobs.