How To Stop My Tank Emptying Itself

[dem0nz]

hey everyone

i am planning on setting up my tank again
its the first time its been used in 2 months as my pictus i kept in it sadly died

what happened was i noticed a slight drop in the water level without any obviouse explanation just as i was leaving to go to work but as i was running a little bit late i just topped up the water and wrote my housemate a note to check the tank when he gets home

a few hours later i got a call saying the tank was drained and my catfish had died

i am using the same tank this time and i have tested it repeatedly to find what could have happened
i have filled it up twice and each time left it to run for a week but nothing has happened
i have an idea of a possability of what could have happened but i am definitly not an expert
so i am turning to you guy to offer any insight you can share with me

the tank is a 6.6gal

i had given it a clean out the day before
it contained a rena internal filter stuck to the side
an internal heater stuck to the side
3 plastic plants (i'm using real plants this time)
a bubble/light tube

and i had added swapped a stone cave for a piece of bogwood during the clean

when i first brought the tank and filled it up i noticed water seaping through the sealant on one of the sides so i took it back to the store to exchange it.
the new one was the same design and i never had any problems with it even after the fish had died

if anybody can think what caused this to happen any input is appreciated as i would hate for this to happen again

 

[aquanovice]

I know this wont help but that is wierd! Are you sure their isnt a leak somewhere and somethign in the tank is blacoking this time around?

 

[gavinlewarne]

I know this wont help but that is wierd! Are you sure their isnt a leak somewhere and somethign in the tank is blacoking this time around?

housemate with a vendetta perhaps (i know its cruel but you never know - seriousely that much water disappearing is just plain weird)

 

[Faythee]

Could the water have emptied by backing out through the tubing to the bubbler ?

 

[dem0nz]

as far as i know there is no leak,when it drained there was no water on the side and since it has been running twice for a week at each time and is now on a fishless cycle in my room i cant see any evidence of a leak

my housemate is my best mate of 16 years and he hadnt been anywhere near the tank until the level had already dropped that day

the bubble tube is the best explanation i could think of,that would also explain why the side of the tank wasnt wet.
i just wanted other peoples opinions on the matter

if anybody has other explanations feel free to post

thank you for your help so far