Replacement of live microalgal diets is a significant challenge in developing cost-effective and reliable production methods for bivalves. In this study, the results of growth experiments are reported with juvenile Manila clams, Tapes philippinarum, fed on a heterotrophically grown, spray-dried, Schizochytrium-based product (SZ; Docosa Gold, Sanders Brine Shrimp) or a spray-dried, Haematococcus pluvialis-based product (H; Sanders Brine Shrimp) either alone or as supplements for rations of living algae. The effects of additions of bentonite, a naturally occurring silt, in combination with SZ and H on the growth of Manila clams were also investigated. Results showed that SZ and H supported clam growth when added as supplements to rations of a mixed diet of the live algae Isochrysis galbana and Chaetoceros calcitrans. Increases in clam wet weight with a 1/4 ration of live algae and a supplement of a full ration (equivalent to the dry weight of the full algal ration) of SZ or H were similar to those of clams fed on a full live algal ration alone. The results indicated that up to 75% substitution of live algae is possible using heterotrophically grown, spray-dried SZ or H without significantly reducing the live (wet) growth of the clams. No significant differences in clam growth rate (% wet and organic weight increase) were found when bentonite was added to diets containing different concentrations of H.