Using pots without drainage holes is never a good idea. The drainage material in the bottom doesn't really help anything.

As you have discovered, there is no way to be sure when you have added enough water because the excess doesn't run out, it just collects in the bottom of the pot. If you add a bit too much each time you water, then eventually the water will rise high enough to rot the roots. If you are cautious and add too little each time, then the lower roots will die from lack of water.

Even if you were to provide exactly the right amount of water each time, there is still the problem of toxic gases building up in the bottom of the pot becaue they have no where to go.

As you can see, using drainless pots is a very risky proposition that may work for a while, but eventually will lead to the premature death of your plant.

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