Runnoff measuring results are not what I expected.

First, use a pot appropriately sized for seedlings. this will fix half the problem. This will avoid the substrate being wet for long periods of time and stangating/growing potentially dangerous microbes / damping off etc.. I like to avoid irrigating until after the seed sprouts. Use a dome to do this, but remove the dome ocne you have a sprout (unless in a desert-like climate, then it may continue to be useful if vented) Fully saturate, plant, use dome to avoid irrigation when the seedlnig has germinated but still plowing through the substrate. By that time the tap root is also down to the bottom of any seedling pot and you can irrigate as normal... fully wet it, wait for dryback, repeat - by the time it germinates, the moisture level will be at a safe level in that regard. Half-watering is a bad idea. It trains superficial roots or causes a drypocket in the substrate which can cause all sorts of problems if it continues to happen over time. runoff is never an accurate measurement, but can still be a useful tool with familiarity. If it's soil, you also have to consider the portion contributing to EC that is not plant available. It can't cause a toxicity inside the plant if it cannot enter the plant... this is the stuff that needs to be broken down by microbs and such before it can enter... leads to higher EC readings that what can actually enter the plant. so, a combination of measuring and observation... to learn what 'normal' is... and if you change soil products or fertilizers, you may need to re-learn normal. So, nothing wrong with measuring, but learn a baseline of what is normal before assuming anything from those readings. Obviously, something is going wrong here and it is a suspect to rule out. you may find it's always an elevated number with the fertilizer/soil you use. If under more ideal circumstances the seedling still looks rough, you can be more confident it's about the soil and not your behaviour. Usually it's our behaviior, ate to tell you. the people that accept that learn and evolve. Those that don't continue to grow ugly, beat up plants. did you get fertilzier water on the seedling? did you have to water before it sprouted -- this will cause the same thing but kinda worse.. the foliage gets saturated with high-dose fertilizer water from physical contact. it's possible this soil is a bit too hot for seedlings, or you self inflicted some sort of damage to that seedling. in the ennd not enough info to help in a specific way..but should be able to step through and deductively rule things out.