Prelude if I were you I would disregard mr. muncheez's advice as quite a lot of it is either false or ill advised. You're in compost so you don't need a pH or TDS meter. You can't measure the TDS/EC of an organic nutrient anyway, so this advice is obviously incorrect for organic nutrients anyway.
You certainly don't
need your water to be reverse osmosis filtered! As long as your tap water isn't rediculously hard you won't run into any problems whatsoever. Millions and millions of people use tapwater with excellent results. Tapwater contains many trace minerals which RO filters completely strip out. If you want to get rid of chlorine vigorously stir it for 10-15 mins or let it sit for 24 hours with an airstone, although, as countless farmers and gardeners will tell you, this is not necessary to get excellent results.
mr muncheez gave a very long list of nutrients and additives, many of which are geared towards hydroponics, which you are not even in. All you need is an organic nutrient for flowering if you're using a fully fertilized compost. That's it. Anything else is not necessary at all and will not give you any more yield if you're environment etc. is not dialled in.
You don't need a grow chart to follow like mr muncheez said. You need to read your plant to see whether it is need of feeding or if it's had too much (e.g. nute burn). That's a far better technique than following some chart made by a manufacturer which are notoriously unreliable anyway. Each strain has differing requirements anyway, making it useless in some cases.
You don't need to flush every third watering - this is rubbish. If you're using organic nutrients in compost you NEVER need to flush and if you're using chemical salt fertilizers you rarely need to flush. Only with severe burning and certainly not 'every third watering'.
Here's a post by Oldtimer1 who has such a good rep on a numberous cannabis boards on flushing with respect to flushing with organics (I can't rememer if you're using mineral salt fertilizers or organic ones):
You can't wash the nutrient reserves from soil, soil based composts or composts except for the immediate soluble salts.
You can,t flush nutrients from plants, you can starve them by just watering them.
My advise if you are using an organic compost, is to alter your feed and reduce the amount towards the end of flowering.
At the peak of blooming you would probably be using 1ml of grow and 3ml of bloom per litre of water. At about the end of week 6 change to some thing like 2ml gr and 2ml bl then 2ml gr 1ml bl then to the end 2 ml gr. This helps maintain the plants healthy right to the end of its life. This gives but that burns sweetly without the acrid taste produced by an excess of phosphorus.
You don't have to worry about the excess of nutrients in when growing with organic nutrients in the same way as you do with chemical fertilisers.
Prelude, you simply need to back off on the nutrients until the burning subsides. You are overfeeding them. Try and get the feeding sorted since issues like this will really affect your end yield and the quality of the final smoke.
Well done so far. On your first grow you'll always run into problems like this. Once you get the hang of it you should run into problems only rarely and even then you'll have the tools and knowledge to deal with them effectively. Just beware of harmful advice that some people give. Unfortunately there are a lot of growers that claim to have been growing for x number of years and to have so much experience when in fact if you analyse their advice much of it is counterproductive or downright harmful to the health of your plants. I would recommend going to a proper growing site like UK420 if you are interested in taking up growing as a serious long term hobby. Poor advice doesn't last long on sites like UK420 (well, UK420 in particular actually).
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