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i live in san francisco, i recently started my pond, it's a 150 gallon pond tub with a 32 gallon trash can an external filter, i have a tetra 1000gph pump submersed on the ground of the pond

air temperature is usually 60-65*, but it will get up to the 70's in the summer and down to the 50's in the winter, is this too cold for 2 adult RES

i have a thermometer in the pond, and it reads 65* throughout the day, and about 60* at night

i would like to raise the temperature of the water another 10 degrees, i currently have a 300w submersible heater inside the trash can but the water is moving so quickly that it doesn't heat it up much at all

i purchased a "pond heater" from amazon and it turned out to be just another de-icer, although it was marketed at a pond heater throughout the listing

What kind of heater is that 300 watt? I would look into a titanium heater, but if the pond has a large surface heater, the heater will struggle to keep the temperatures. You might just want to set in a deep calm area and your RES will find it. 65F should be OK for healthy adult RES.

This pond is outside right? You dont need to be heating the water ever then. Actually you can cause alot of harm trying to keep water warm while temps low outside. The turtles will be fine year around even with water temps falling into the 50s.

Yes, you will not need to worry about heating your pond. I live in Huntington Beach and my 2 sliders have survived 5 winters with no winter heating. They just sleep on the bottom until springtime, occasionally waking up and surfacing during warmer winter days.