Great question I need the forums help with:
I just finished with my first plant(AK47) and the yield was only around 1.5oz. I have a tent, mars 300watt, five gal bucket. I used17-6-6 for vegetative, 30-30-40 for flowering. Seeds germinated Jan 15. Did four weeks vegetative stage with 18 hours of light. Switched to 12 hours and added flowering fertilizer. Quality was about a 6 on a ten scale. I stopped using vegetative fertilizer week six. Flowers started showing three weeks after I went to 12 hour. Ready to start with my next plant but would like to do better. I split the stem four days before harvesting. What am I doing wrong? thanks
With out the knowledge of your last grow
Pictures of plants etc your question is a bit tuff to answer
I recommend you start a grow journal when you start you next grow so you can post pictures and questions on problems that you might be having during you grow so we can guide you to a successful harvest
Make sure you use properly ph’d water is the best suggestion I can make at this time
If you start a journal and have a problem you’ll receive all the help you need from the great folks that read and participate here on the best forum around
Happy growing CB
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30-30-40 seems a little high in nitrogen, especially in flower. Were the leaves clawed and very dark green? Nitrogen toxicity can prevent buds from developing fully. When you go to flower you want the lowest N you can find. Something more like 0-30-40.
If you buy a quality growing medium, that alone should have enough nitrogen (N) to get you through veg stage; and you probably won’t need to add any more (N) for the rest of the grow. Concentrate on the PK through flowering and your pH. 
@Countryboyjvd1971 is right.
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As @majicmarkers said the 30-30-40 seems pretty high in nitrogen. Typically you want a fertilizer with a higher middle number (phosphorus) early in flower then Switch to a higher last number (potassium) in the final couple of weeks. Some people use the same fertilizer throughout the entire flowering phase and add a supplemental fertilizer which contains a higher last number. (In Veg you would want a higher first number (nitrogen))
The extra nitrogen in flowering might have stunted your bud growth slightly.
Really though it is hard to say without having all the particulars.
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Pretty much everyone read my mind and caught same detail I did
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