it cannot be understated jeff-keeping mixed species together can be fatal-its not just the toxin issue (which i dont believe can be solved by filtration), its also the aggression they have towards other species or even in some cases with each other, in captivity these animals are kept in unnatural concentrations (outside of breeding season)-water quality isnt the reason they stay in lower concentrations in the wild.
all newts/sals have teeth, but size of teeth isnt the issue-many can exert a higher limb/flesh shearing capacity by just clamping on to another and spinning like an alligator till the flesh gives way -or the limb pops off (or is de-sleaved, meaning the flesh is pulled off the bone)
it is worth noting that though we like to give human traits and feeling to our animals, newts arent given to such things as 'pouting', the orientalis ran away and hid, because the other made him fear more damage, in captive conditions they have less to fear and are less likely to be territorial due to the abundance of food offered on a regular basis-but this doesnt mean they will not fight, or just mistake anothers limb for a food item.
it is not just random advice from 'do gooders' that causes us to repeat-ad nauseum-the advice of not mixing species. many of us-before having access to such things as the internet- have kept species in such conditions and ended up with dead newts as a result. sometimes they can go years w/o issues then all the sudden 'snap', i personally have had 2 pachytritons kill each other, i also had pachys bite legs off of tiger salamanders. some displays in zoos have mixed species exhibits and give the impression of 'harmony'-they do have as much harmony as in the wild and will occasionally eat each other. i asked a zoo keeper about the displays and he says they just replace the missing animals when this happens. most exhibits, however, put species together that are from similar areas and might interact and have avoidance mechanisms adapted for those species-your 2 species however are from a globe apart and not likely to have such behaviour established for dealing with each other.
you can believe they are fine if you so wish-but you must realize that your belief is just that, a belief, supported with data modified to fit it. you can do as you see fit-but do so with full knowledge of potential consequences.
p.s. tigers dont have sharp teeth - i would let one bite me easily, dicamptadons have teeth sharp enough to easily draw blood-i can speak from expierence here.
