Ever since I added a few drops of fertililzer to my plant tank, the pH went from 7.4 to well over 10!!!!!!!!!!!

The tank is well buffered.....same as all my other tanks. I can find no other changes or reasons that this should be, so the fertilizer it must be.

So.......what do you'all do?

I don't know on the fert, but I doubt that it raised the pH.

In a planted tank, you will get pH swings daily.
carbon dioxide (CO2) is an acid.
During the day when the lights are on, the plants consume CO2 and produce oxygen (O2). At the end of the day your pH will be higher because the plants have used up the CO2 in the water.
At nite, the plants consume O2 and release CO2, so first thing in the morning, your pH will be lower because of all the extra CO2 in the water.

The fert may have an indirect effect by increasing plant growth and use of CO2.

I'd check pH first thing in the morning and again at nite to see how much of a swing you're getting.

Do you have any fish in there?

I have two adult guppies and a set of 2 week old fry - about a dozen or so, a clown loach (1 inch) and a siamese algae eater(2 inches). It is a 10 gallon tank, Aquarclear sponge filter 60gph probably (it is old) , 7 plants plus java moss. It will be upgraded to a 20 long or 30 gallon tank in a week or so. The plants are growing very well. The fish seem healthy. It has .1% salt. No airbubblers. The only additions I have made are 20% water change every week or so with enough salt to keep the tank at .1%. And the fertilizer - 3 drops from an eye dropper as per the bottle instructions. The water is quite hard - and was very well buffered. I cannot remember the numbers at this time.

I will test this morning and evening. I will not fertilize again until next week. I shall see where the tank goes in the interim. Luckily, the fish and plants do not seem to be too stressed by this - I am more bothered, it seems. I just do not like things to change without me changing them......

I haven't used flourish liquid, but I do use the tabs, and they haven't affected my pH. The box says that they won't affect pH, but in soft or poorly buffered water they may have an slightly acidic effect. I assume the liquid would be the same -- if it affected pH at all, it would be to lower it, so I doubt the fertilizer was the culprit. My pH varies throughout the day, but I've never had such a large variation as 7.4 to 10! Can plants cause that much of a variation?

what is buffering?????

I have the liquid fert... will this help my plants??? My eldora keeps going yellow and then the fish eat it all...

On the bottle is says u can give a small dose daily or a larger one weekly.... which do u sugest is the best???

buffering
There are carbonates in your water that keep acids from making the pH drop (get more acid). That's what KH measures.