As a general rule, if the strength of the salt content in your grow media (which we will call the E.C) exceeds that of the salt content in your plants roots and stem, then moisture will be leeched out of the plant rather than in. This happens irregardless of whether or not you have the pH correct, or your feeding regime is every 3-4 days. Pots can dry out just from the often low humidity in a grow room so it is not an indicator that plants are actually absorbing via the roots.
Nutrient retailers often define plant problems in terms like nutrient lockout and deficiencies because to them they want your every response to be to go buy some other additive. Growers have taken on this language, but it is not true description of what is really taking place.
Down in the bio level of your plants, its salinity, and acidity that determine uptake of water, and the nutrient that has attached itself to the water molecules. Roots either uptake water, and the nutrient that is dissolved into the water, or they leech water and nutrient that is dissolved in the water. Leeching often leads to wildly swinging pH or acidity levels. When acidity is too low, nitrogen is unable to be released from media leading to nitrogen deficiency. When the acid levels are too base or alkaline, potassium and phosphorous are not released from media particles leading to deficiencies.
As you can see, if you are keeping track, merely feeding more nitrogen when you have a nitrogen deficiency, where that deficiency came from a pH swing that was caused by too much salt content in the grow media which caused plants to leech nutrients rather than uptake them, feeding more nitrogen is merely adding more salt to the media, making things worse.
To self regulate the salinity without having to use one of those expensive EC soil test meters, feed every second watering, and every other time you water, just use plain old water and flush water, which means feeding enough water through that there is significant runoff. Drain this runoff away and you will prevent salt from building up around the roots.
In doing so you will also find the pH, and/or the acidity stabilizes. Swinging pH is often a sign that roots are leeching moisture rather than taking it up. With the leeching moisture is also nutrients that is carried in the moisture. The longer this happens the quicker the nutrients build up in the root area, nutrient buildup is a fancy term for high salt.
To fix a problem that has caused a deficiency, flush your media out with fresh water. In this case, give it a thorough flushing.
