If one 300 watt will do the job, the second one is for redundancy and temperature stability. The 75 will will do nothing. Remember heaters are not additive.According to the aqueon heater chart, their 300w can raise up to 90g up to 15 degrees warmer than room temp, so if you get two of those that leaves an unheated 10g if you want to raise the tank 10 degrees above room temp. If you need a really warm tank, I'd do 2 300w and 1 50-75w, if you don't need to warm it that much 2 300w should do the job
Uhhh... no. That's like saying 2 cars are faster than one.I don't quite follow that. If one 300w is rated for 90g, then shouldn't 2 heat 180g leaving an extra 10g?
Yes, that's what I mean for stability across your tank. Placing the heaters at difference ends of the tank and having good water movement is a must in that situation. For redundancy if one fails the other keeps the tank at your temperature (or at least that one half).Ok, I think I got it now. Does that also mean the only reason for multiple heaters would be for consistency? As in 1 heater probably wouldn't evenly heat all 4 feet of a 4 foot tank?
OK, now for the real world. Finding 2 of the exact same heaters that work identical? Well not really. One may heat to 5 degrees more than the other, happens a lot.Gotcha
If you have two heaters set at 80, they will not raise the tank to 160, just 80. 1 heater will have to be on a little bit more, but the amount of heaters doesn't change the temp the water can get, just how hard each one has to workHeaters do have a cumulative effect, they are able to raise a maximum of X degrees above current temp by maxing out their wattage. (X being unique for each heater, usually around 15 degrees.)
This is why putting the same heater on a 50-degree tank would raise it to 75, but on a 70-degree tank it would get it to 85. On the first tank it would run continuously, but on the second it would cycle on and off to keep it steady.
Having two heaters in the same tank will increase the heat by the total watts combined, because both will run in tandem until the desired temperature is reached. One may kick on before the other because of tiny differences in the built-in thermostat, but since it won't be strong enough to heat the entire water volume enough to where it would cycle off again, the second will kick in once the water cools a bit to trigger it, and both will heat together until the desired temperature is reached and then they'll kick off again.
I see what you are saying, but they dont make a lot of 1000w aquarium heaters, so the op needs to run multiples on their system to achieve the desired temp.If you have two heaters set at 80, they will not raise the tank to 160, just 80. 1 heater will have to be on a little bit more, but the amount of heaters doesn't change the temp the water can get, just how hard each one has to work