help trigger & eel death?

[nanoreefer]

ok this a long one but, for the last three months ive had a 3" V lion and 2.5" niger trigger in a 10g QT tank wile ive been working on there 75g tank(lots of problems with it!)two weeks ago i added a small zebra eel and they were all eating and doing well, on tuesday i got my new aqua safe aquarium RODI untit and hooked it up then i did a WC wendsday moreing useing the RODI water the SG on my hydrometer read about 1.027 or so but it has gone higher than that many times so i wasent worried, i whent out on wendsday and bought some macro and red algea for a seahorses tank i was working on and put it in the 10g, i was planning on moveing the fish from the 10g in the next few days and useing the astablished 10g for the SHs wile i finish there tank, thursday the eel and lion woudent eat trgger did, but i figured they woudent sence i added the algea and they were getting used to it, friday afternoon the trigger was dead never looked sick or anything just dead, the eel dident look to good listless and just sitting half out of the rocks, i did 3g WC and the eel looked better but was dead at 10PM, the lion seemed fine and is still ok but dident eat any food until yesterday i have n=never tested the water before but iam sure it has been worse yet the trigger and lion were always fine and the eel ate well dos anyone have any ideas what might have hapened the only thing i can think of is there was some disease on the algea or the RODI water sence there the only things i changed on the tank? but now it has realy shaken me up sence most of my LR was in there and now i dont whant to use it for the SHs if is contaminated or diseased

sorry for the long post i just whanted to list everything and try and get an idea what i did wrong, aside from the 3 fish in a 10g thing i know that