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
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If its 250 to 500 GPH - then definitely go with the shingle 1/2in RFG flow kit
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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
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if you have any questions, you can call us as well - always happy to help
623-233-6908 - support