RH avaeraging 40-45% and have dry leafs any advice

Hi

using 300w led's, strain 3 x kc 36, babies are 4 weeks old now but showing signs of having yellow on the edges of the leafs which are very dry, any advide please?

sorry no pics yet ill sort it out soon

You provide very little info but...

How close is the LED? Most should be 12in+away from the canopy or they can burn leaves.

The dry leaves could also be nutrient burn.

The RH is a little low for veg and it would be good for your plants to get it up to 50 - 60% but that's just a positive tweak and isn't the reason that your leaves are very dry.

sorry the led's are about 10-12 inches above plants, we only give them half the nuits required . the soil doesnt dry out until 3/4 days so watering could be eratic

whats the easiest way to increase the rh to 50-60%

I increase RH with a humidifier that I purchased at walgreen's. You can do it to a lesser extent with a cloth dipped in water so it wicks the water and a fan blowing on the cloth.
If you are going half notes (and you aren't using miracle grow soil or something elseof the like with all kinds of nasty fertizilers in there), then it's probably not nute burn. You might need a bit of nutrient deficiency - try some cal mag or a teaspoon of epsom's salt in a gallon water.
Sounds like you may just need to water a little more often. I check the soil by putting a finger into the soil up to the second knuckle. If it's damp, no water, if not then get out the watering can.

Just hang in there and keep working it