hi ecro
i have a biorb 30 too,def dont bother doing anythin till u get back,and as gazpug says there is no need to put the heater on till you get back either as it wont start to cycle just by leaving the filter going for 3 weeks, you will need to start the cycle either fishless ( link above) or with 1 fish,doing tests and water changes etc for a period of 28 days before adding another fish ( or 2 depending on size of fish) also remebering to de-clorinate the new water ( only the amount you replace and not the whole 30l)then its a weekley chore (15-20% water change)
but remeber that the biorb stores all the good bacteria in the media (craggy gravel in the base) and therfore the filter sponge and media(inside filter pot) need to be changed approx every 4 weeks,and dont take the gravel out to clean it with soap etc, if it does require a wash, do it in the water you have taken OUT of the tank, not tap water
i only have 1 siamese fighting fish in mine and thats all i intend to keep in there as i dont think they are suitable for much else personaly,there is a member on here ( forgot his name) who keeps ornamental guppies in his and he has great success with them,so dont be put off at all by my opinions
also i dont know if you will have the same with yours, but my heater tends to be a bit tempramental in that it is set to one temprature then heats the water to another,but that may have something to do with the halogen light in there, so make sure you use a reliable thermometer,so you know whats happening
have you read the book that came with the biorb, i found it to be very useful,very similar to the advice on here but to the dimensions of the biorb.
you should be able to add your fish after 24 hours of heating the biorb up (75 +/- depending on fish) but be carefull to remove the bubbles off the acrylic ( with your finger or algae cleaner) as they can cause problems such as pop-eye in your fish
what did you plan to keep in there,i would be very interested to know
and even better,when you get back from holidays,put some photos on,love to see what your doing, heres mine,its in my bedroom so i only really get to see it at night (shame) but i really enjoy watching it, even the bubbles are relaxing lol,if i can help you further just ask ( im not an expert, but ill do my best
)
shelagh xxx