no need for more fans if you go water cooling, in your case, just place the fans on the rads
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Let me add, custom water cooling is not what you have in mind, i guess what you have in mind is a modded antec khuler, custom water cooler involves lots of stuffs from cpu water blocks to your gpu water blocks to your fittings to your adapters to your tubings to your res and to your radiators and specifically on your fans, not just a normal led fan would do a great job in cooling down a radiator, it needs a good static pressure for dense rads, and lastly for custom loop, a deep pocket