help:leaves browning yellow at the edges, why?

hey all, so these are in coco, temp is about 25 degrees, 3 weeks into flowering using canna a+b nutes, a couple of days ago the leaves started going yellowish on the edges it seems to be getting worse. i don't know what it is over fed under fed???
sorry about the crap photos

Potassium (K)
Potassium is involved in maintaining the water status of the plant and the
tugor pressure of it's cells and the opening and closing of the stomata. Potassium is required in the accumulation and translocation of carbohydrates. Lack of potassium will reduce yield and quality.
Potassium deficiency:
Older leaves are initially chlorotic but soon develop dark necrotic lesions
(dead tissue). First apparent on the tips and margins of the leaves. Stem and branches may become weak and easily broken, the plant may also stretch. The plant will become susceptible to disease and toxicity. In addition to appearing to look like iron deficiency, the tips of the leaves curl and the edges burn and die.
Potassium - Too much sodium (Na) displaces K, causing a K deficiency. Sources of high salinity are: baking soda (sodium bicarbonate "pH-up"), too much manure, and the use of water-softening filters (which should not be used). If the problem is Na, flush the soil. K can get locked up from too much Ca or ammonium nitrogen, and possibly cold weather.



Figure 13


Figure 14

Potassium (K) Toxicity:
Usually not absorbed excessively by plants. Excess potassium can aggravate the uptake of magnesium, manganese, zinc and iron and effect the availability ..



this is in the faq!! looks a bit like this? take a gander yaself m8 its useful. gd luck

hey i got a plant growing with a red heat lamp and my leafs are curling rite when they start to grow any advice i dont know how to post pics im new to here

click th emanage attachments tab, under the rply box to post pics m8... when my leaves were twisted it was dwn to a high ph causing nutrient lock out. check ya run off and post some pics im sure someone will help,, aslo u best off starting a new thread by going into the indoor growing section and clicking on new thread button at the top of the list of threads gd luck