watering and feeding

so am nearly in week 4 of veg stage. i have 2 white widow plants under 600watt mh bulb. there growing in kana terra professional soil the plants are between 12" to 18" tall. reading up on a few threads in here i have come to the conclusion that i have been giving my plants nutrients everytime i water them which is every other day. on 1 of the plants the leaves have formed brown spots and alittle yellowing on the tips. i have just gave them water today no nutrients. the questions is (as im new to this) how often should i water and how often to give them feed? i currently water them just before the lights go out and thats most days and with terra grow feed.

ok so if your growing in soil u dont want to water that much..thats probably where the brown spots are coming from..how big is your pot?? and how big is your plant?? if you got a nice sized 2ft plant it probably needs water every 2-3days but smaller ones like 3-5days..lots of people think one nutrient will make them grow these awesome looking plants but u need more then a base or one additive..this is what i use for just VEG..GENERAL HYDROPONICS- Micro, Grow, and Bloom..Bontanicare's Liquid Karma ORGANICARE'S-Seaplex, Huvega, and Humega and last but not least the best product out there Hygrozyme..o yea and sometimes i add a little carbo load in veg

my pots are 3 gallon 1 plant is 22" tall and the other is 17" tall. so if i water them every 2 days should that be with the nutrients or 1 time with just water and the other with nutrients? i didnt realise i would need all these nutrients so i shall go to my local grow store and ask for advice and other products i need. cheers for the advice cali.grown

Use a moisture meter (cheap/walmart)....I feed my plants an age appropriate bio bizz with ever-increasing strength with every watering once they hit the flowering tent. Mine are in 4" pots.....which requires checkin' them daily for their needs as they seem to change size so quick....