Hydroponic nutrient is not the way to adjust PH. You need acids and bases to adjust PH. Acids to lower PH and Bases to raise it.

how do I do that?

Contact the people you bought your nutrient from and get a bottle of Ph UP. This should be an alkaline solution.

But, why are you using distilled water? That is an unnecessary expense. Most people use ordinary tap water that has a Ph of 6.5-7.0. You can use swimming pool acid to bring the Ph down to around 6.0.

What are you using that dropped your ph down to a 3? I use dynagro and it normally drops down to 4.3-4.6, I solve this by using a pinch of magnesium sulfate, dash of calcium nitrate and a couple flakes of potassium hydroxide.

I would use a different nutrient solution, but if you are going to use this, then use some potassium hydroxide to bring the ph up to a more comfortable 5.5-6.5.

I would also suggest RO water instead of distilled water. The machines are pretty easy to install.

CYA
Okami