Jason, welcome to the forum, we are glad to have you as a valued member. When you water your seedlings, water them throughly, so that 10 percent of the water drains out the bottom of the container. Never water your trees on a prescribed schedule. Water ONLY when the tree requires additional moisture. Depending on the size of the container, water when the top 1 inch or 2 inches of the medium feels dry. Personally, I do not like using water meters. Water meters have killed a lot of trees. Learn to ascertain when to water by the weight of the container, or by using your finger. Young seedlings frequently are killed in the first two months by stem rot, caused by the fungus rhizoctonia. To help prevent this, water your trees only in the early morning, then set the container in the sun to quickly dry the surface of the medium. Rhyzoctonia, thrives in warm moist environments, therefore the sooner the top of the medium dries, the safer will be your pants. You can begin to fertilize at 1/2 rate as soon as your seedlings develop their first two true leaves. Fertilize a MINIMUM of once a month, twice a month is much better. I fertilize my older trees with every watering. You did not mention whether your fertilizer also contains trace elements, trace elements is an absolute must. Further, with every 3rd watering you will need to add magnesium (Epsom salts), at the rate of 20 percent of the nitrogen applied. I am not familiar with the 3-1-1 citrus/cactus mix you are using. I only use a 4:1 CHC/peat moss mix. However, if your medium is RAPID draining, you will not have to excessively worry about over watering. Good luck to you and your tree, -- welcome.
Regards,
Millet
Thank God for Massachusetts January 19, 2010