Do You Think This Is Ok

[typhoon]

have been getting my tank ready for discus since november now, the water is correct i know that, and i am picking up 10 juvie discus at the end of the week, but i just want some suggestions or opinions on wether my tank can handle whats in there.

its a rio 400 tank with an external 405 and a sand substrate
there are amazon swords in there
20 glowlight tetras
5 corries
9 clown loaches
1 goldy plec
1 common plec
3 german rams.
i think my stocking is okay the guy im buying the discus off has bred discus for alot of years and says ppl are too picky with discus as after all the years and the in breeding and tank breeding there alot tougher these days, but still though id ask what you guys thougt
now its not overstocked as such as it is a big tank but im thinking filtration wise what do you think? ill be changing approx 100 litres a week, but would it be wise to stick another external 205 or even the smaller one on there??

thanks

thanks luke