How can i Tween a thirst GUI?

I am making a Survival game that includes hunger and thirst gui

here's the code for the hunger which works perfectly apart for the color change part

local HG = script.Parent
local num = HG:WaitForChild("Back"):WaitForChild("NumText")
local Text = HG:WaitForChild("Back"):WaitForChild("Text")
local Plr = game.Players.LocalPlayer


repeat wait() until Plr.Character

local Hum = Plr.Character:WaitForChild("Humanoid")
local MaxHunger = 100
local DecreaseRate = 25 -- 8 seconds = -1 hunger
local HungerValue = HG.HValue

HungerValue.Changed:connect(function()
	Text:TweenSize(UDim2.new(HungerValue.Value/MaxHunger,0, 1,0), "Out", "Linear", .2, true)
end)

while wait(DecreaseRate) do
	if HungerValue.Value - 1 >= 0 then
		HungerValue.Value = HungerValue.Value - 1
	end
	
	HungerValue.Changed:connect(function()
	num.Text = HungerValue.Value
end)
	
	if HungerValue.Value == 0 then
		repeat wait(1)
			Hum.Health = Hum.Health - 2
		until HungerValue.Value > 0 or Hum.Health <= 0
	end
end

if HungerValue.Value < 41 then
Text.BackgroundColor = BrickColor.new("Daisy orange")
end

if HungerValue.Value < 21 then
Text.BackgroundColor = BrickColor.new("Persimmon")
end

if HungerValue.Value < 11 then
Text.BackgroundColor = BrickColor.new("Really red")
end

and here is the script of the thirst which is somehow defective

--First the variables
local Thirst = script.Parent
local Thirstval = Thirst.Value
local Back = Thirst:WaitForChild("Background")
local Tbar = Back:WaitForChild("Bar")
local Plr = game.Players.LocalPlayer
local hum = Plr.Character.Humanoid
local MaxThirst = 100
decreaserate = 30
local num = Thirst.Label
--wait till the character loads
repeat wait() until Plr.Character

while wait(decreaserate) do
	if Thirstval.Value - 1 >= 0 then
		Thirstval.Value = Thirstval.Value - 1    --reduce if it isnt 0 or below
	end 
	Thirstval.Changed:connect(function()
		num.Text = Thirstval.Value     --update the text indicator
	end)
	if Thirstval.Value == 0 then
		repeat wait(2.5)
			hum.Health = hum.Health - 2.5   --reduce the health if its 0
		until Thirstval.Value > 0 or hum.Health <= 0
		end
end

Thirstval.Changed:connect(function()
		Tbar:TweenSize(UDim2.new(Thirstval.Value/MaxThirst,0, 1,0),"Out","Linear", .2, true) --tween the bar indicators
	end)




-- this is frustrating

I don't get why it isn't working, can someone pls tell me what I'm doing wrong?

There are few problems with your code. Consider this expression: wait(decreaserate). If you read about wait(), you will find out that it returns actual time elapsed before the task scheduler resumes your code. So its never false nor nil, therefore you have the infinite loop there. This is causing two serious issues.

First issue - following code will never be executed:

Thirstval.Changed:connect(function()
        Tbar:TweenSize(UDim2.new(Thirstval.Value/MaxThirst,0, 1,0),"Out","Linear", .2, true) --tween the bar indicators
    end)

Connection is never made, because the interpreter is stuck in this infinite loop.

Second issue - you are making new connections for the same function everytime the loop is repeated:

    Thirstval.Changed:connect(function()
        num.Text = Thirstval.Value     --update the text indicator
    end)

This small function connected multiple times will probably not cause significant lag, but after a while you may start to notice flickering. Remember, you only make connections ONCE! Lua will not throw an error for repeating connections, because more than one connection is allowed.