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What's the best water heater you can use for 70-100 gallon stock tanks?

visi therm stealth heaters are really good.

I agree I have the 250 watt heater for my75 gallon tank and it keeps the temp really nice and even. It only cost $20 at petsmart (print out the price rom online and they will match it) I have an aquarium, not a stock tank but I have touched the heater to see how hot it gets and I don't think there is any reason to think it won't work in a stock tank.

I've been using Ebo Jagers in stock tanks. They are made of glass and it's therefore wise to place them in a heater guard, but they worked really well last winter.

The visi therm stealth heaters have a plastic coating, so you don't have to worry about it being broken by turtles.

I agree with a Marineland Visi therm Stealth. I have a 250 watt in my 55 and it does a great job.

But the 250 watt is only recommended for tanks up to 75 gallons, so after that, you want to consider getting 2 of them or what Marisa suggested.

We also have a Marineland Visi therm Stealth for Spike's new tank, based of course on recommendations from this website/forum! The aluminum core with thermal plastic exterior and competitive cost make this a great heater for a turtle tank (although you didn't specify what you were planning to put in the stock tank).

I would suggest, based on my tropical fish tank experience, that you consider 2x250W heaters for large tanks to ensure more even temperature control, although that may not be necessary for a turtle tank.

Just my 2 cents...