I recently bought a 35 gallon hex tank that came with rock heater filter adn a bunch of other stuff. The filter is a Penguin 125b, i researched it and it is discontinued but i was still able to find filters online. My question is will this heater work for my tank. On there website i found that a Penguin 150b is rated to 30 gallons. so is my Filter only rated to 25 gal. Any help would really be appreciated!

Sounds like your filter isnt going to be enough....

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"Being ignorant is not so much a Shame, as being unwilling to learn".-- Benjamin Franklin

Your heater will suffice, but it will be running a lot more than a heater rated for your tank, or a heater rated above your tank. If you're ok with a slightly higher power bill, then I would say you're in the green. Eventually, however, the excess wear and tear from almost continuous operation will necessitate that you buy a new heater, so keep that in mind before your current one breaks, because if it breaks you run a good risk of cooking your fish or electrocuting them.

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Officially fishless until after the move....tune in later for details!

I apologize Gizmo. i said heater when i ment to say filter. the heater i have will work just fine just curious about the filter. Sorry!