The queenstown diving pool is open for scuba diving and freediving. 4.5m max depth.
Our freediving instructor organize pool training there and can also book it by yourself. It's a great place for training.
Last month my friends and I book it via email for freediving. The manager was very friendly and let us train there for free as promotion. Normally he charges 10sgd for freediving and 25sgd(not very clear) for scuba diving with weights and a tank. He told us he would control the number of divers so the pool wouldn't be overcrowded.