Quote Originally Posted by gainesvillegreen
What are you using to adjust your pH? If you're using 'over the counter' products (like vinegar or baking soda), it's possible what you're using isn't strong enough to properly buffer the solution. Correct this by purchasing commercial pH up and down products.

The problem could also be your hydroton. Many people experience problems with pH fluctuations when using hydroton, especially if it is not treated before use. Stinky had recommended somewhere that you take all your hydroton and throw it in a bucket with some water and a very diluted nutrient mixture (say 15-25%). Put an air pump and a stone in the bucket and pH the solution to what you desire. Check it every hour or two and continue to adjust it until you don't see any significant change for hours (a day would be better).

The pH'ing process above can take a while, days even, but I can attest the efficacy of the process.
Hydroton has no influence on ph hints why its the number one choice for grow median.Now if your using rock wool yes this will affect your ph and you should let it sit in ph water over night.