i used to spray my clams with 250W and no chiller...only cooling with fans...temperature around 28 most of the time...guess it shouldn't be a prob...
for clams, dun forget the calcium and kh that they require...i had 2 croceas in my old 3ft tank, i supplement them with kalk only...no money to buy CR...so dose kalk everyday...of course my evaporation is super high, because i use fans...3-4ltr per day...
clams grew well, i think...and survived with me for about 4-5mths before i sold them away...grew at least 3 "folds", dunno wat is it called, extra shell??, watever....
IMO, clams are light dependant, so if u are thinkin of PL, quite dangerous...t5, i would say place them as high as 4inches below water level...
just my opinion lah...still up to individuals..