That is EXACTLY what you want to see. That means that right now, as of today, she is happy with about 370, so I'd go with approx 350 ppm until it starts dropping again. Keep in mind, that you will not see improvement in existing leaves. Your upper growth should look great however. Also, get a PH pen you can rely on. Your current one might just need calibrating. Drop it in some CAL 4.0 and if see if it reads 4.0. Distorted leaves usually indicate a micro nutrient deficiency. It is usually can be caused by PH lock out, however in this case, I believe it to be too little nutrients until just last 48 hours.
Remember, just 48 hours ago, you only had PPM at 150. Give plant time to adjust. If you have some SuperThrive, add a 1 ml per gallon (1/4 tsp)
Your PPMs are going to fluctuate, your plant is a living thing. You should not have been frustrated that your PPM rose overnight and here is why.... When your lights go off, photosynthesis stops. The plant quits producing energy and begins to store it and make it available for cell construction (growth). This process requires water and the plant takes it from the reservoir. The plant isn't utilizing nutrients like it does in light, therefore the volume of water intake will be much higher than the nutrient intake. Because water is removed from the tank, but not nutrients, the nutrient's parts per million value increases because the water decreases. Does that make sense?
right now, you are in that new grower phase of fear and consternation. try to realize that most adjustments need to be minor. Most mistakes that kill plants are dumb ones. Over reactions, trying to many remedies, over analyzing your plants. Try to remember that it is a weed. It is very versatile. (most strains are, but not all). RELAX and chill
there is nothing wrong. just keep at it with the ppm like you learned. small adjustments. If you don't believe a reading, take a new sample and test again. Also, hydroton does not change ppm or ph. it is completely 100% inert. That is why it is the most popular hydro medium....