What is Reddit's opinion of Phresh Carbon Filter For The Cleanest Air Around, 6" x 16" - 400 CFM?

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What lights are you using?

If it's current-gen LED, you should be fine with a 4" inline, and 4" Phresh filter. If not, 6" inline and one of these.

I don't know that it's the best "bang for your buck". But cheap fans and cheap filters, are, well, cheap. Fan is the most important part of your grow. If your fan goes, your plants die in hours. Filters, IME, either do an okayish job for a cycle or two (Vivosun, Apollo, iPower), or they do a great job for 1+ years (Phresh).

Phresh Filter 6 in x 16 in 400 CFM - 701005 https://www.amazon.com/dp/B004FVJK60/ref=cm_sw_r_cp_api_28OHyb8CGGXC8

PHC Enterprise SC-3M Variac Variable Transformer, 300 VAC Max, 0-130V Output, 3 Amp https://www.amazon.com/dp/B006NGI8VS/ref=cm_sw_r_cp_api_69OHybP25VE6Y

This is what I have. Works great. The variac does not hum at all. I have the vortex as well.

Saw your other comment about odor concern, try adding:

http://www.amazon.com/Phresh-701005-Carbon-Filter-16-Inch/dp/B004FVJK60

http://www.amazon.com/VenTech-VT-DUCT-6-Aluminum-Ventilation/dp/B00DCES1TI

http://www.amazon.com/Stainless-Steel-Ducting-Clamps-Ventilation/dp/B00MJ5G8YQ