Mid season leaf problems

I have been growing various things (including bonsai) using Canna coco coir as a growing medium. It's nice in that over a year it doesn't change in volume. It seems to stay nice and airy around the roots too. The only problem with coco is that it can cause a shortage of calcium - hence the special coco orientated fertilisers. I didn't understand until I did some more research.

http://en.wikipedia.org/wiki/Coir

I started to see leaf curl on my habanero chilli plants - so I did some research. I bought some calcium nitrate fertiliser off Amazon. I added this to my organic fertiliser and I haven't had a curled leaf since. The vitality of the chilli plants has increased as well.

Now I am growing some Scots pines in this same growth medium so maybe they have the same nutrient issues? I gave them a dose and they seem to be a bit more perky.

I now understand why their nutrients come in 2 parts - the calcium and potassium form insoluble precipitants in the solution if they are too concentrated. So I know they are looking after the calcium issue. I am using the soft water version of the fertilisers - so I should be OK. But something still seems to be wrong.

The calcium nitrate has fixed my citrus up nicely - and my cherry no longer has lacy leaves on its second flush. I have a Pyrus pyraster (wild pear) which is also giving much better growth with this treatment. So far, so good.

In the summer when it's warm I use organic fertilisers and rainwater. This may be negating the effect of the specialised nutrients looking after the calcium issues with coco growing mediums.

My copper beechs have a lot of burning on the leaf edges. I'm unsure if it's salt or the hot weather? I am fairly certain that this isn't the calcium issue affected the fruiting/flowering trees in coco coir soils. These are in my experimental very large pots. I water these with tap water because I just don't have enough rain water to go around. The beechs in clay based substrate are much better off - but they tend to get the rain water by hand and not the garden hose.

I tested the pH in my rainwater butts and it was off the scale of my test kit - so well less than a pH of 6. I have bought some hydroponic pH stuff to take this up a little as it can affect the beech roots. I will also test the soil acidity to understand this problem better. I will aim for a pH of 6.0 - 6.5 as this gets rid of the aluminium toxicity problems.

This is really annoying as June/July are the months when the beech will give its peak growth.

In addition my poor oaks have terrible powdery mildew - it's really ruining second flush this summer. I have sprayed this with milk (diluted 1-10) and will report back on the success of this treatment method. I have ordered some systemic fungicide just in case - but I prefer the milk spray if it works.

I am wondering if my low fat milk works as well as full fat ?