Basically, both plug-in instances are identical but the current Acqua engine can work with long audio buffer or without any audio buffer.
The instance without audio buffers, zero-latency or just ZL, does not have any audio buffer pre-loaded and will process the audio without any delay, so at the same time CPU load will be higher compared with standard non ZL instance.
The idea behind a ZL instance is to give users the option to run Acqua Effect products with minimal latency, useful for example for direct monitoring.
To contact Acustica Audio support go to the ‘Support and Help-desk Section’ in your Acustica Audio account. We do not provide support via social networks, public forums, Acustica Audio forums, or email accounts.