Set one up for my nephew last year, so here is exactly what I did and what it cost.
Tank: 2 feet, about 60 litres. Not a bowl, not a 1-foot "starter kit". Bigger is genuinely easier, and this is counter-intuitive to everyone — more water means slower changes in temperature and chemistry, which means more room for a nine-year-old's mistakes. About Rs 4,500 with a lid.
Sponge filter + air pump. Rs 1,200 or so. Cheaper than a hang-on, no risk of a small fish being sucked in, and it holds bacteria beautifully.
No heater. A Lahore room sits between 22 and 30 most of the year, which suits guppies and platies fine. Saved money and one thing to go wrong.
Cycling — and this is the part I did differently. I did not make a nine-year-old wait four weeks staring at an empty tank. I seeded the new sponge with squeezings from my own established filter, which cuts it to about a week. If you do not have an established tank, ask at a decent aquarium shop — many will give you a bit of used media, and the good ones understand exactly why you are asking.
I still made him test the water every day and write the number on a chart on the wall. That turned the boring part into the interesting part. He now understands what ammonia is, which is more than most adults in this hobby do.
Stocking: six guppies. Six. Not twenty. We added six more after a month. Every child wants to fill the tank on day one and that is the single most common way a first tank dies.
Feeding: once a day, as much as they finish in about thirty seconds. I gave him a tiny measuring scoop because "a pinch" means whatever a child wants it to mean. Overfeeding is the second most common way a first tank dies.
Total: about Rs 9,000 including fish, food, conditioner and a test kit.
A year on: the fish have bred twice, he has given guppies to three friends, and he has lost two fish total. He is far more interested than he would have been in a bowl with a goldfish in it.
What I would tell anyone setting one up this weekend: buy the tank, the filter and the test kit this weekend. Buy the fish in ten days. That single change in order is most of the difference between a tank that works and a tank that is empty by Eid.
