Yes, there is a much better treatment. The products you have chosen will only "burn" the plants back. If you were to choose this treatment, you should substitute Reward for the Weedtrine (Weedtrine is a watered down version of Reward).
I would suggest Sonar being used instead of the products you have mentioned. This is a systemic product that will kill the entire plant. It is expensive, but worth the price.
Are you sure you have hydrilla? This is a rare find since California has a very aggressive treatment program when it comes to hydrilla. If you think it is hydrilla, you should bring this to the attention of the state for proper identification.
