My usual long answer:
pH is probably the number one cause of problems to the newer grower but they often don't know it. After using most tap water for six or seven weeks the soil will lock in a pH that is roughly the same as the water. If you've added lime to the soil or otherwise stabilized it with some form of calcium or calcium/magnesium agent you are sunk at this point and there is no good solution, flushing or otherwise, except to start over properly. Your plants will yellow prematurely from nute lockout, which many people mistake as the normal course of flowering, but it's not. Only the large fans should turn yellow in flowering, all the new growth should be green and healthy up until the end.
So...
You MUST check the pH of your water (after adding nutes if adding any) and adjust to around 6.0 - 6.5 if necessary. Tap water is almost always 7.0 or above sometimes in the 8's. Bottled water is usually in the same range.
Get a digital tester ($50 or so), not strips, they are a pain and too subjective to be accurate. Use a pH adjusting agent made for plants not pools, use something like Earth Juice Natural Down (down because that's the direction you almost always need to go with tap water) and not lime juice or vinegar because they are not stable after a few hours. Some ferts will take your pH down to where you need it without adding anything else - Tiger Bloom does this with my tap water.
Hope this helps. I learned it the hard way.
pH is probably the number one cause of problems to the newer grower but they often don't know it. After using most tap water for six or seven weeks the soil will lock in a pH that is roughly the same as the water. If you've added lime to the soil or otherwise stabilized it with some form of calcium or calcium/magnesium agent you are sunk at this point and there is no good solution, flushing or otherwise, except to start over properly. Your plants will yellow prematurely from nute lockout, which many people mistake as the normal course of flowering, but it's not. Only the large fans should turn yellow in flowering, all the new growth should be green and healthy up until the end.
So...
You MUST check the pH of your water (after adding nutes if adding any) and adjust to around 6.0 - 6.5 if necessary. Tap water is almost always 7.0 or above sometimes in the 8's. Bottled water is usually in the same range.
Get a digital tester ($50 or so), not strips, they are a pain and too subjective to be accurate. Use a pH adjusting agent made for plants not pools, use something like Earth Juice Natural Down (down because that's the direction you almost always need to go with tap water) and not lime juice or vinegar because they are not stable after a few hours. Some ferts will take your pH down to where you need it without adding anything else - Tiger Bloom does this with my tap water.
Hope this helps. I learned it the hard way.