Can Anyone Please Help Me Asap Mt Plants are Hurting

What up all so hers the deal im in week 4 of flower and im growing some skunk 1and it is starting to not look so good , So my leaves are starting to yellow from the out side of the leaf inward and only betweenthe vains and now there getting these littel black dots all over the leafs they dont look like but and i have no idea what to do or what it is . Im useing a flood table and water 3 times when the light is on and only wet the roots once at night . My timps are 80 max during the day and 70 to 75 when its on my humittiy is at 20% to 30% and i change my Res every week and use the flara nova nutes and my ppm is at 900 in week 4 of flower my Res temps are good at any where from 65 to 70 and would love for any any to poot in on this im all for some ideas . So please Help i relly need this to pull through

are the black dots bugs?
any nutrients?

Need no hps lights pics please. If you need help we need good pics. Thanks

Flush and re fill with pure water. 45+/- PPM..You are high at 900 PPM in week four. I'd think you be down as you near the end. You leaves curling inward is a text book example of over fertz..Good luck. The flush is the sure bet to fix...Side on to less fertz then too much fertz..