New Salt System, algae is recurring regularly

[chem geek]

Let me clarify a few points since there are some conflicting pieces of information or conclusions taken from my threads. As was noted, SWCGs produce hydrogen gas bubbles. If you don't see them during the day when the SWCG is on, then set it to operate at night with pool lights on and you'll be much more likely to see the tiny bubbles.

The production of chlorine in an SWCG is the same as adding hypochlorite to the pool so it raises the pH when the chlorine level rises. However, the usage/consumption of chlorine is an acidic process that exactly counteracts this effect so if one is maintaining the FC level then using an SWCG is pH neutral. There are other ways that the pH can rise including carbon dioxide outgassing. This is why lowering the TA level can help since it relates to how much the pool is over-carbonated.

As for reducing scaling in the SWCG cell, it's not just the TA but maintaining a slightly negative saturation index (say, -0.2) that can help. Using 50 ppm Borates also helps because it cuts the amount of pH rise near the hydrogen gas generation plate roughly in half.

There are other ways the pH can rise including curing or degrading of plaster, but also if chlorine gas from the SWCG doesn't fully dissolve and outgases instead. This can happen with short pipe runs from the SWCG to the pool. To minimize both the increased aeration from the hydrogen gas bubbles and the amount of potential undissolved chlorine gas outgassing, a higher CYA target (with proportionately higher FC target) can reduce the chlorine loss from the UV in sunlight and let one turn down the SWCG on-time.

As for the pH effect from Trichlor, as others have noted, the effect will vary depending on whether the pH would be rising if Trichlor were not used. Nevertheless, for every 10 ppm FC added by Trichlor it not only increases CYA by 6 ppm but also lowers TA by 7 ppm (after accounting for chlorine usage/consumption). If one doesn't replenish their TA level (or have significant evaporation and refill with water high in TA), then the TA can get to zero and the pH crash which can cause pretty serious damage.