Can I use a pool ionizer alone in a hot climate?

Not really. Ionizers reduce chlorine needs but aren’t a replacement for an oxidizer in hot climates where algae thrives. Copper and silver ions kill algae slowly, and hot sun speeds growth, so you’ll still need a small chlorine residual (1–2 ppm) or regular non-chlorine shock to avoid green water. Think of an ionizer as a helper, not a set-and-forget solution.