Tank Heater

Hello Eddy and welcome

Heaters are not that accurate in my opinion so don't panic yet.  I'm sure somebody with more experience will be along to advise.

In the meantime, are you doing a fishless cycle.  I ask because although it's a second  hand tank you have replaced the media so it will no longer support fish very happily?

What are you thinking of putting in the tank

The temperature settings on heaters are often inaccurate, it's best to rely on a good thermometer to find what the tank temperature really is. Most heaters also have an orange light to show when it is on, if the light is permanently on then the heater is still trying to reach the set temperature, if it goes off before the temperature is reached then it is probably inaccurate settings on the thermostat.

What is the room temperature? Heaters are rated appropriate for tank size if the ambient (room) temperature is "normal", but if a tank is in an unheated room it might need a more powerful heater to maintain the required temperature during the colder parts of the year.

It is annoying that you set the heater to the temperature on the dial, and subsequently find the actual temperature falls way short.
It's a shame they can't calibrate them better, but I suppose we'd have to pay significantly more.

Quote

In the meantime, are you doing a fishless cycle.  I ask because although it's a second  hand tank you have replaced the media so it will no longer support fish very happily?

Hi Sanjo, Simple answer is....Yes I am. I bought "Interpet New Aquarium start up kit" and I am on day 3 of the cycle, I have completed 1 water quality test so far (obviosly more to come) and water quality is good.

Unfortunately, that isn't a fishless cycle. You need to add ammonia for a fishless cycle. The start up kit you mention contains a bottled bacteria product and more than likely will do nothing leaving you doing a fish-in cycle with all the hard work that involves. Your water quality should be excellent as you haven't yet added a source of ammonia, either from a bottle or fish excreting it.
This explains what a fishless cycle is.

The start up kit seems to contain:
A bottle of Fresh Start, a dechlorinator which also removes heavy metals. You need this, all water added to the tank needs to be treated with a dechlorinator. When the bottle runs out, you can choose from many different ones.
A bottle of Filter Start. This is the bottled bacteria, and probably won't work as you might think. Very few of the bottled bacteria products on the market do anything.
Test kit. What exactly does this contain? One sites says pH and nitrate, another says pH and nitrite. You need ammonia and nitrite, pH is a good idea and nitrate maybe.


As regards your fish list, you might find the rainbowfish a bit active for a 61cm tank. And you may have problems finding flag cichlids. I've only ever seen them in one shop. Be flexible on these, maybe look at apistogrammas instead. The easiest to keep are cockatoos and agassizis, both in the cichlid section of the fish profiles.
And two female guppies will turn into a lot of guppies very quickly. Female livebearers like guppies can store sperm for around 6 months, and give birth to a batch of fry every month for 6 months without a male. If a female guppy has ever been in a tank with a male for longer than about 2 minutes, she will be pregnant when you buy her and carrying sperm 

Another factor to consider is the hardness of your water. Your water company's website should have that info, though they may give a bewildering assortment of units. You need to look at German degrees or mg/l CaCO₃ (aka ppm). If they give them both, even better.