In order to investigate the effects increasing of total hardness in water on rainbow trout (Oncorhynchus mykiss) and lettuce plant (Lactuca sativa) growth indices in an aquaponics system, 90 rainbow trout fishes and 260 seedlings of lettuce were randomly introduced into 9 experimental unites. Treatments were affected by increasing the total hardness (calcium chloride) concentration of 0, 100 and 200 mg per liter of water (total 140 mg of total water hardness) for 60 days. Growth indices of fish did not show significant differences (P≥0.05) among treatments, but survival rate showed a significant difference between treatments (P<0.05).  Plant growth indices such as leaf length, leaf width, plant fresh weight, plant dry weight, root fresh weight and root dry weight showed significant differences between treatments (P<0.05). The results of blood biochemical indices showed that increasing the total hardness in water, treatment with 100 mg of calcium chloride per liter of water, showed the highest concentration of calcium of the plasma as 11.36±0.25 mg/dl, showing a significant differences compared to other treatments. Other blood indices such as hematocrit (Hct), mean corpuscular volume )MCV(, hemoglobin (HGB), red blood cell count (RBC), mean corpuscular hemoglobin (MCH) and concentration of red blood cells (MCHC) were not significantly different (P≥0.05) between treatments. The results indicated that adding 100 mg L^-1 of total hardness to water (meaning 240 ppm to water), have a positive effect on the biological conditions of the plant and fish in an aquaponic culture of rainbow trout and lettuce.