hi,i wrote a reply to you about the john innes compost and didnt realise you had loads of replies already !!! sorry for being a num nut,but anyway,i had a set up with this particular compost about 6 years ago and i had it set up for two years,i read that your dreading having to dirt your tank in 6 months or a year but i got some good news regarding that,you might not have to do that because if your looking afte your tank right and keep dirt debris at a minimum youll find that in a weird way the compost and the gravel just get better with age,i think its got to do with stuff breakin down in the compost like fish waste and plant bits that get left behind even after cleaning up,i found my substrate just got more fertile as time went on,but i did use tablet ferts inserted in substrate and also used liquid ferts once a month.good luck with your set up anyway kind regards_Rebaka