Its important to remember that fitting these fans will DEFINATELY increase the temperature in the hood, which in turn will DEFINATELY reduce the life of your bulbs and DEFINATELY increase the temperature of the water.....
T5's optimum operating temperature is room temp (around 25c), the hood gets a LOT hotter than that already, and reducing fan airflow will obviously increase the heat...
Ive done very similar tests on the hood fans, and found that cleaning the standard fans reduces noise significantly.... the noise comes from the fans sitting too close to the grills of the hood, if you remove the fan from the housing and plug it in - its silent.
Im not doubting that the PC fans are good quality and probably do run more quietly than the standard fans, but they push
significantly less air, and as a consequense you will have expensive bulb replacements much more frequently.
Its also worth pointing out that you can fit 2 extra fans in the hood as there are spaces already there, and these then push cool air over the ballasts.
My outcome was not to use expensive 'quiet' pabst PC fans I bought and stick with the red sea ones, but clean them thoroughly, I did add 2 of the pabst fans into the hood as extras though. I also removed the 2 water cooling fans and installed 2x80mm noctura fans. My tank now runs at 26.5c with no chiller (down from 29.5c!!). Ill probably junk the pabst fans and get 2 more of the standard red sea fans to go in as fans 5&6, or I migth try the water cooling ones in there as they also flow much more air than the pabst ones.....
Heres a cut and paste from my tank thread on another forum (note: I actually ended up using the 2 standard fans and 1 pabst fan in the end)
Here is the right hand side. You can clearly see the extra housing at the top where an extra fan can go quite happily:
theres probably enough room to fit 4 fans if you cut out/remove the housings......
heres one of the (filthy) standard fans:
and one of the new fans:
height comparison:
and heath robinson testing with iphone db meter app.... first up, the 2 old fans:
now 1 new fan, 1 old fan - as you can see 12db drop from changing 1 fan..... if only they pushed more air....
and finally what I went with, 1 old in the centre:
And lastly, heres how to cleanup the standard fans. Firs off peel back the sticker and remove the rubber grommet:
then push the axle in the centre through with a screwdriver, leaving a small circlip and a rubber o ring:
you can then get all the crud and dirt off the fan and housing ready to refit. Just push the fanback through till it stops, the refit the o ring and push on the circlip.
I really think its wise to fit extra fans as there are 3 ballasts in the hood which would benefit from aitr being blown over them:
And heres the water cooling fans:
2 cable ties hold them tightly together, and another 2 hold them roughly in the right place at the back of the tank. Ive unclipped the regular fans, and removed the connector for the 12v outpu, and used this to connect the fans, so they are controlled byt he normal fan switch on the RSM.
Im glad to report that temperature with the tank on as normal amd the fans on all the time is a steady 26.5, which is I suspect is the temp my heater is set to
This may not all be down to the fans though, as Im also trying to maintain the water level at 6 notches down as per the red sea site guidlines.... ther only problem with this is the noise of the water falling from the weir (ie removed all the sponges) - far noiser than the fans ever were... Ill try to add more water and see if I can find an acceptable level
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Happy to report that they are silent!
Here they are against the standarcd ones, which incidently are RDL6015S