I mentioned the water because that looks close to chemical burn in my experience - chlorine or chloromite in the city water and/or pH buffers etc. Regardless - that kind of response appears indicative of toxicity of some sort - like HushPuppy mentioned.
I've surely been incorrect before however and in this case if I am - your issue is likely calcium as Growdude implied. When we flush plants for what-ever reason, one of the first nutrients to wash away is calcium. As we know, water consists of 2 hydrogen ions and one oxygen molecule (H2O). Hydrogen naturally will replace some important minerals such as magnesium, calcium, phosphorus and potassium. In the majority of standard mediums, water molecules combine with the available carbon dioxide forming a weak acid, known as Carbonic acid (H2CO3). This weak acid reacts to it’s environment by ionizing or slowly separating and binding with other elements of the medium. When carbonic acid (H2CO3) contacts calcium it releases it’s secondary hydrogen ion and carbon ion. This hydrogen replaces the calcium particles in the medium first. The now released calcium binds with the carbon to form calcium carbonate. Calcium carbonate is soluble and leaches from the medium. All of these reactions slowly acidify the medium. After calcium, alkaline elements like magnesium become soluble and can leach as well.
After flushing midway through a cycle its important to replace minerals that could (and will) be washed out. A mild dose of (chelated) cal/mag may help. Those spots are permanent, but production should not be too effected.
Good luck