Toilet tank looses water over time

Toilet tank won't fill up or is slow to fill. The most common reasons for a valve to slow down or no longer fill the tank after the flush are debris issues and the length of time a valve has been in use. ... Valves in use for a period of 7 years or more can have their working parts start to wear out. 1.
https://www.fluidmaster.com/toilet-problems/remove-fill-valve-cap-replace-seal-toilet-wont-fill-slowly-filling-tank/

Your best bet is to get a new Fluidmaster fill valve assembly at the hardware store and follow the instructions in the package. While you're at it, you will probably want to get a new toilet connector hose (just so you will have nice new gaskets that won't leak) and a new flapper (flush) valve for inside the tank. The flapper valve seats into a round, plastic valve seat that sometimes gets all junked up with calcium so that it doesn't seal well, allowing water to leak down the drain and causing the fill valve to let more water in periodically. You should clean off the surface of the valve seat so it is nice and smooth. I use my hands and a rag for this because I don't want to gouge the surface with metal tools, damaging it.

the fill valve is not letting water in you either have a float that raises up when water is full so when you flush the float drops down letting water in then when water raises it shuts off i would replace the float fill valve and corky flapper.... here is what you do .... first shut water off where it goes up to the tank....... flush commode to empty as much water from tank....... reach up under tank there is a plastic coupling that connects the water supply line to the bottom of the toilet tank...put a small pan under the shut off valve that goes to the toilet some water is going to drain from the tank when you take the coupling loose..... turn the coupling counter clockwise ( use a channel lock adjustable wrench to loosten then had turn) once this is loose you can pull the riser tube away from the tank...... now there is a plastic nut that screws the shaft to the bottom of the tank loosten with channel lock then remove with hand by turning counter clock wise ( you will get a bunch of water flowing down to the pan) remove the entire fill valve , replace with a fluidmaster fill valve ( about 8 bucks from big box store when you take the new fill valve out of the box there is a neopreme seal you must put on the new threaded shaft ( it has an inner ring you may have to punch out) once you put this on you can insert the entire shaft down through the hole in tank then secure with thin nut provided tighten but do not overtighten then put coupling back on,,,,,put the over flow tube on the tit of the fill valve and stick down into over flow ok thats done when you go to big box store purchas a 5 buck corky flapper (red caus it can handle chlorine water better) remove the old one at bottom of tank( just two clips to remove and chain attached to flush lever...install new one be shure chain does not have a lot of slack so it does not fall under flapper seal when you flush......OK YOU ARE DONE TURN WATER ON WATCH TANK FILL LOOK FOR LEAKS TAKE A TOWEL AND DRY ALL AREAS THEN TAKE YOUR HAND AND FEEL FOR LEAKS UNDER TANK AND DOWN TO SHUT OFF VALVE .....CONGRATS YOU DID IT!

By leaking do you mean onto the bathroom floor, or is water escaping out the flush valve (the part that the Hydroright is seated in) into the toilet bowl. If the former 1) check toilet tank mounting bolts/gaskets for deterioration or looseness. These are usually 5/16"x3" brass bolts with rubber, plastic, and metal washers with a nut. They can be seen protruding through bottom of tank. 2) check flush valve and rubber gasket between tank and bowl. The flush valve is the one that the refill tube goes into and the hydroright seats into.
If you are only leaking water into bowl I would suggest the blue dome gasket ( part of Hydroright kit) is not properly seated properly into flushvalve, and you may have to re-install hydroright (the instructions explain how to remove and re-install) . I broke my existing/old flush valve at the base when trying to install my Hydroright so maybe it was fortuitous that it broke and I had to install a new one. Hope this helps.

Turn off the water to the fixture.

Flush the toilet and hold the handle down to let as much water out of the tank as possible.

Sponge the rest of the water out so the tank is dry.

Remove or undo the water supply tube from the fill valve.

Remove the three bolts holding the tank to the bowl and remove the tank.

Replace the old seal with the new one and reverse the whole process.

You should be good to go.

Good luck.

Sorry for problem with new toilet.
You say water is leaking out of the bowl?

Toilets have 2 parts:
1) Tank: where water is stored for the flush and is sealed with a flapper.
2) Bowl: where water flushes down.

a) If tank is leaking water, then flapper is suspect. Replace flapper and see if that works.
Lift up flapper and run finger around rim to see if there is a rough spot that would indicate flush valve is defective, and needs replacement.
See typical flush valve

b) If bowl is leaking, that is very unusual and would indicate a crack in the porcelain.

If installer sold you the toilet, it is his responsibility to make good on product.
All products are guarantee against workmanship flaws.

Is the flapper valve slow to return to the closed postion allowing water to flow through the flush valve? Make sure the toilet flapper is moving freely and is sealing properly against the flush valve. If there is no lengthy or continual water flow in to the toilet bowl then this is not the problem.

Is the water valve on the water fill line to the toilet tank fully open? This may seem silly but it could be this simple.

Check to make sure your fill valve is opening fully. If you have an older toilet there may be some deposits that need to be cleaned way to allow free movement.

If toilet does eventually fill to the desired level, there is no leakage, water valve on fill line is fully open and fill valve is opening fully then recommend you shut off water supply, drain toilet and disconnect water fill line from the water valuve and toilet tanke to make sure there is not a blockage. If the water line and connections are clear you may need to remove the fill pipe in the tank and check for blockage. If this is very old, conisdering the cost and effort, it may be simpler to replace at this time rather than trying to extend the life.

If your hooked to city water it can be cause of the high water pressure comes across and keeps flapper from seating rite. Take a empty plastic bottle,cut it in half long ways. flush toilet then place plastic bottle between fill valve and flapper,trying to devert water away from where flapper seats. good luck.

I have minute amount of leakage into the bowl causing mold to grow. I believe that it may be the rubber seal for the flapper body to the porcelain.

get a new filler assembly. the water in the tank is heavy enough to close the seal completely. or the rubber seal is not making contact. thats' why the leak.
change the whole assemble ususally correct the problem.
adjuste the flow to about 1/4 to 1/3 under the over flow. if that still don't give you the pressure. you ca adjust the flow tube to 1/5 under the cover. that is the max.