diff --git a/src/service/disinfection_ctl_service.cpp b/src/service/disinfection_ctl_service.cpp
index a7faf17..c0818af 100644
--- a/src/service/disinfection_ctl_service.cpp
+++ b/src/service/disinfection_ctl_service.cpp
@@ -83,7 +83,7 @@ float DisinfectionCtrlService::getDisinfectionDValue(float ppm) {
 
   if (ppm < 150) {
     dvalue = -0.5251 * ppm + 98.154;
-  } else if (ppm >= 150 || ppm < 240) {
+  } else if (ppm >= 150 && ppm < 240) {
     dvalue = -0.125 * ppm + 38.913;
   } else if (ppm >= 240) {
     // 240  -> 8.913