You dont need to go crazy over high temperatures. Nano tanks are absolute heat-absorbers meaning that they can get their temperatures rising almost instantaneously when left without proper ventilation or equipments to cool the tank down. This is something inevitable in dealing with a nano tank. but, even though it's such a sucker for heat, it's also a big fart when it comes to releasing heat from its waters. Just a simple fan or an open window can cool any nano tank down. It's something cheap and efficient especially the latter.
You do not need to situate your tank directly beside the window and let it expose to nice cool air. Just a nice spot, away from direct sunlight will do the job just nice.
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fans wise. There are many types of fans around in the market. You dont need to just look into metallic framed fans or aquarium fans to give you the ventilation across the water surface. Fan is fan. There isnt any classifications for fans, so just look for one that's plastic lorh. there are alot around. and I promise you there are way more cheaper than those you get in aquariums.
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lightings.(I believe your tank's almost 40cm ba, slightly more than 1ft) If you want to keep zoos or mushrooms, you dont need PL light to give them their necessary light supplements. FL or T5-Normal Output can do the job liao. T5s are also cooler and FL will be cheaper on the long run, and PL light tubes users usually experience a faster shift in their light spectrum from crisp white to yellow in 6mths or so. well Since there are alot of 1ft with legs extension lights in the market. Go C328 and walk around. You should be able to find some, or maybe Petmart in Serangoon will be closer to you and do a change eh? a 27W PL light? well, save it for your refugiem ba. Too hot and inefficient for a nano tank.
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if anyone says that FLs cant keep zoas and mushrooms, well I can challenge that. Aint scared man. haha
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20W is a nice wattage for a big tank, but not for a nano tank when heat issues are such a concern. Honestly, I will recommend you to go for a Sanders Picolo for a nano. It's airstone driven, but it eliminates you a heat source. 20W is nothing for a big tank, but it's a degree or two rise for a nano tank.
Nano tanks need patience and guidance. It's not your type of conventional tanks, which you dump money inside and see results quickly. It takes time to grow and time to maintain. If you lack the two aspects, don keep a nano reef. Keep a species tank instead, like a pipefish specialise or boxfish specialise tank. jsut dont go heavy on reef. but if you want to, you can too. Just look into the alternatives and try it out. It's less than a hundred bucks mod. wont burn a hole in your pocket, instead you may end off with a beautiful soft corals tank at the end of the day.
anyway I am leaving you with just that. I'll monitor your thread.
If you need help, just pm me. I'll call you.
ta!
all the best for your new tank.