diff --git a/src/ZSOLVER/tridiag_thermo.f90 b/src/ZSOLVER/tridiag_thermo.f90
index 95e86abe02d31200869309a613f7b86efe447094..7ba28585cf889c05a029487228b15e8dcdc5a908 100644
--- a/src/ZSOLVER/tridiag_thermo.f90
+++ b/src/ZSOLVER/tridiag_thermo.f90
@@ -380,19 +380,15 @@ END DO !CONCURRENT
 !
 !$acc loop seq
 DO JK = IKB+KKL,IKE-KKL,KKL
-   !$acc loop independent collapse(2)
-   ! acc loop gang, vector collapse(2)
+   ! gang+vector needed or parallisation vector only
+   !$acc loop independent gang, vector collapse(2)   
    DO CONCURRENT ( JI=1:JIU,JJ=1:JJU)
-   !DO JJ=1,JJU
-   !   DO JI=1,JIU     
       ZGAM(JI,JJ,JK) = ZC(JI,JJ,JK-KKL) / ZBET(JI,JJ)  
       ! gam(k) = c(k-1) / bet
       ZBET(JI,JJ)    = ZB(JI,JJ,JK) - ZA(JI,JJ,JK) * ZGAM(JI,JJ,JK)
       ! bet = b(k) - a(k)* gam(k)  
       PVARP(JI,JJ,JK)= ( ZY(JI,JJ,JK) - ZA(JI,JJ,JK) * PVARP(JI,JJ,JK-KKL) ) / ZBET(JI,JJ)
       ! res(k) = (y(k) -a(k)*res(k-1))/ bet
-   !   END DO
-   !END DO
    END DO !CONCURRENT 
 END DO
 ! special treatment for the last level
@@ -411,8 +407,8 @@ END DO !CONCURRENT
 !
 !$acc loop seq
 DO JK = IKE-KKL,IKB,-1*KKL
-   !$acc loop independent collapse(2)
-   ! acc loop gang, vector collapse(2)
+   ! gang+vector needed or parallisation vector only
+   !$acc loop independent gang, vector collapse(2)
    DO CONCURRENT ( JI=1:JIU,JJ=1:JJU)
       PVARP(JI,JJ,JK) = PVARP(JI,JJ,JK) - ZGAM(JI,JJ,JK+KKL) * PVARP(JI,JJ,JK+KKL)
    END DO !CONCURRENT