Sharp PH drop after nutes!!!

Hi, I have just filled up my nft 40l tank for the 1st time, ph was 7.6 then added my ionic grow hardwater 250ml slightly less than recommended waited an hour took the ph and it came out at 3.6!!!!! Is this sort of drop normal the ec looks ok about 1.3, but just don't understand the sharp drop in ph. If this is normal I will just adjust with some ph up but wanted to get you guys thoughts??

Thanks

my tanks does the same thing when its in fill cycle my ph drops to 6.0-3.0 in that range. Although the ladies still look good anyways mane.