It will depend on your return pump, and your aquascape
If your return pump is 150 to 300GPH, then I would suggest the dual 1/4in Random Flow Generator® Nozzle flow kit
https://vividcreativeaquatics.com/s...k-return-line-upgrade-kit-1-2in-to-1-4in-rfg/
If its 250 to 500 GPH - then definitely go with the shingle 1/2in RFG flow kit
https://vividcreativeaquatics.com/shop/1-2in-random-flow-generator-flow-kit-1-2-flex-series-rfg/
With that said - if you rockwork is tall ,and would block a single 1/2in RFG when pointed diagonally across the tank, then regardless of the pump size - go with the dual 1/4in
You'll find them on our website and at all major online retailers. But, you may also find these flow kits at you local fish store - so check there first :)
https://vividcreativeaquatics.com/where-to-buy/
if you have any questions, you can call us as well - always happy to help
623-233-6908 - support