Please look at pic of leaf tips curling, on older ...

hey there MG , these leaf curls are indicative of root problems. That's because you're not using a chelation agent to break down the nutes so they are creating adverse microbial life that is affecting the roots making the leafs curl. What you can do is use a chelation agent like enzymes or humic or fluvic acid to break down the problem roots and help the solution recover. Otherwise hydroguard is a synthetic option, basically it's 1% hydrocloric acid and it breaks down anything alive in there and it will help you fix the problem. You can use it during the flush too ! hope this helps ! 🚀