Mottled brown spots on flowering plant? (pics)

[Fringey]

I have a few White Russian plants which have been in flowering about 5 weeks. in the last few days one has developed brown spots on the leaves which are getting worse. There are two colours two it, a light brown sort of mottilng and little darker brown spots. There are also more yellow leaves lower down on this plant than on the others. Also, to my eyes, the plant directly next to it seems to have more yellow leaves as well and may be showing the first signs of the brown spots. But I could just be being paranoid about that.

All the plants are clones from the same mother plant and have been in exactly the same conditions throughout.

Couple of shots of one of the leaves below, a bit blurry but you can see the different colour. This leaf was taken from the top section of the main lead. Does anyone know what this might be?

[SmknVTEC]

Could be a few things. Could you give us some more details? What type of lights? What type of fertilizer you feed it, how often and when was last time? Do you know the ph of the soil? If not, check it. What type of soil is this? At 5 weeks, you have about three weeks left of flowering or so on White Russian.

[Fringey]

It's a 250W HPS light. I use canna terra flores at the reccommended dilution rate every other time I water, which is currently every other day. The soil is sterilised top soil with perlite and vermiculite added to improve its consistency. Haven't checked the soils pH, but I'm pretty sure the soil is pH balanced and I'm certain the nutrient solution is.

[SmknVTEC]

The only reason I ask is because your plant looks like it has a calcium deficiency. Calcium is often locked out by the wrong ph. I would certainly test the ph. It is the first thing one does when a problem arises. Does your fertilizer have micronutrients in it?

[Fringey]

Right, that's the second forum I've had that answer, I'll test the pH. Is that likely to happen to one plant and not the others though when they're under the same conditions? I gave them water only for a few days because I thought it might be an over-nutrient thing but it hasn't really seemed to make any difference. If it is that how do we fix it? Add calcium? Or flush?

[MynameStitch]

can you take another picture of it? its blurry

[Fringey]

Sorry, my camera's not brilliant that close up.

Here's a slightly better shot of the leaves, I had to take this one in the cupboard and the lights washing out the colour's a bit.



I'm going to get a pH kit at the weekend. In the meantime, I noticed the plant next door had started to go slightly as well, but the pattern of yellowing and where the dots are worse seems to be where the light was falling most intensely, so I've raised it quite a bit and I'm flushing with filtered water only for a bit to see if the new growth stops showing these signs. Seems the best thing to do until I can test the pH.

Here's an overhead shot, I was hoping it would show where the yellowing is but because of the orange light you can't really make it out. The plant on the far right is the worst and you can just about make out the one next to it is starting to go.

[SmknVTEC]

It is best to take pictures of the plants under natural light especially when there is trouble. Definitely get the soil ph strips and maybe some hydro ph tester so you can test the run off of the water.