Underfeeding or PH?

Hey guys so everything has been going great up until switching my nutrient solution to Flower stage( I am using 3 part Flora Series from GH) about 48 hours ago. This is week 2 of flowering.

The top growths on all my plants are yellowing while all other is healthy.
Also one Airstone died so the smaller plant had no oxygen for around 12 hours. Just wondering if I should give them more nutrients or adjust the ph up from 5.8 ( i am growing in a DWC system) or just give them time to adjust?

Also these pics are 24 hours old the yellow has gotten much worse on the small plant

Dude hurry and make a new batch. They won't die, but it can cause defects in growth and yield amount. Flush the pebbles for about 20 mins, to make sure your salts are all out of there. You need some type of oxygen for the nutes, they need to be aerated. They need to be, no getting around it. This time try around 3/4 of what the dosage says. Your pH is fine. Before you switch nutes, after you flush the pebbles real well, fill bucket with fresh water, and let your plant sit and drink off of that for about 30 mins, then switch it out. Always give fresh water in between. They look to good for you to lose them right now. Cure that nutes burn and get it oxygen and keep nutrient aerated.