Anyone know what is going on with my avocado tree last year it was fine i grew it from a seed but this year the leaves have suddenly started browning and dying off and at first i thought i was over-watering and it slowly got worse so i thought i was under watering and still no go.
Whilst I'm no expert, as far as I am concerned if your avocado's tap root is either wet or impeded you are susceptible to all sorts of problems. This is why people build large mounds above the ground and plant their avocado in it. Also young plants are susceptible to sunburn, if you are in tropical climates, sub tropical you are OK
You were probably right all along. It was over watered. The damaged caused below the surface is often not seen above the surface until much later. This goes for the problem being corrected as well. You fixed the problem by watering less, but the leaves continued to show damage. The leaves are still reacting to the damaged roots from being over-watered. It take time for the roots to recover, during this time the leaves are still going to show you there is a problem, because the plant is not yet completely recovered.
Never water on a schedule water when the plant needs water. There are various techniques to figure this out. You could soak the pot really good, then lift the pot and take note of the weight. The pot will lighten up as the water is used or evaporates. You will be able lift the pot in the future to know if it needs more water.
For some people like myself, we have problems judging weight we need other techniques to know it the plant needs water. I use a bamboo skewer. You insert the skewer in the soil for 30 mins. After that time you take the bamboo skewer out. You look at it and feel it. If the stick it wet do not water. If the stick is completely dry you weighted to long and need to water asap. You want the stick to come out slightly moist, but not wet, cool to the touch.
Those are two techniques there are more. Moisture metres can not be trusted, unless you spend the money to get a nice one. If you citrus soil has lots of drainage matter, that drainage matter interrupts the signal. The device might think the soil is dry, but it is actually wet.