Regarding the heater issue - could your heater just be undersized for your tank? Is the heating light continuously on? I ask because it sounds like your temperature stayed constant even though you turned the heater up, which sounds like the heater may already be working as hard as it can. There are some factors in addition to the size of the tank that affect how many watts heater you need, the most relevant one being the temperature differential between your house and the tank water. Other less notable factors are air flow around the tank and proximity to a home heating unit vs exterior wall. Your heater will wear out faster if it is always working at its peak capacity, so you may be better off getting a second auxiliary heater to help the main heater. I personally always believe in having at least two heaters per tank, because if one breaks, the temperature will decrease much more gradually and gives you time to fix the situation without shocking the fish.
Also welcome to the forum I am looking forward to following along on your fishkeeping journey!
Hey thanks for the input.
So the tank was a deal with the filter and the heater so I would have assumed that it was the right one.
Ive put the heater up to maximum now but it's only budged from 21.1 to 21.4c so not really a huge increase. I'm also not too keen on putting two heaters there as I'm running out of plugs under the unit - also the light goes on when I turn the dial up then it turns off which is I assume when it hits peak temp.
We do also have a pump but that doesn't seem to affect the temperature.
I'm off to get some plants so hopefully that will help with the life of the tank a little bit.
Thanks!