Cold water is one of the underrated causes of slow growth in winter. Tap water arrives at around ten degrees, and giving that straight to the roots stalls uptake for hours: the root zone has to come back up to temperature itself before anything starts moving.
Which rating for which tank
The three AquaKing Aqua Heaters are not three versions of the same thing but three volumes. The HE-200 is meant for 100 to 200 litres, the HE-300 for 200 to 300 and the HE-500 for 300 to 500. Choosing too light means the element runs constantly and still never reaches temperature; choosing too heavy is not a disaster but is unnecessary, since the thermostat switches it off once the value is reached anyway.
All three with a thermostat and a plastic sheath
The thermostat is built in, so you set a value and leave it rather than switching the element yourself. The plastic protection around it is why these heaters can also go in a collapsible tank: no hot glass or metal rests against the fabric. That is not a detail, because a large part of the range under Water Tanks is exactly that.
Warmer is not better
Aim for around room temperature and no higher. Warm water holds less oxygen, so you trade one problem for another as soon as you overshoot. If instead you are running a system that gets too warm in summer, you want the opposite, under Water Chillers, and you read the temperature itself with a meter from Measuring & Control.
Frequently asked questions
How long does it take to warm up?
That depends on how cold the water comes in and how large your tank is. More practical than waiting is leaving the element on: the thermostat holds the value, and then your supply is ready whenever you want to water.
Can the element end up running dry?
That is what you want to avoid. A heater belongs under water, so keep an eye on your level in a tank that drains into a system, and switch it off before you empty the tank.
Do I need this if my room is heated?
Usually not for the tank itself, since it comes up to temperature on its own. It matters mainly in a garage, shed or cellar where the temperature drops far overnight and your tank follows the room.
