Still Stuck, Stuck, Stuck, Stuck..........

Check the water everyday and if there's any ammonia or nitrite or the nitrates are too high do a water change and that should solve the problem, I  think you'll be ok though and CONGRATULATIONS!!! 

I do 2 small water changes a week just enough to hoover up the poo really, about 25% weekly should do it.

BUT

If you find you have ammonia or nitrite or high tank nitrates when you've got your fish in you may have to do anything up to a 75% water change depending on how high the readings are. I got a bit anal about testing water after I added new fish and did it x2 a day for the first week until I was sure the filter bacteria could cope.

You need to change your signature AM, you've got fishies now 

Nope I meant the

"90 ltr Betta Lifespace tank with 88 ltrs of unstable water : ( "

Well i will carry this thread on for a few more days, till i know my fish are "permanent" lol so
 Day 46  (day 2 of fish in) Ammo = 0 Nit = 0   (two fish very lively, on just hiding  )

Day 1 Ammo = 0.25 Nitrite =0 
Day 2 Dosed tank with Ammo up to 3ppm
Day 5 Ammo = 1.00  Nitrite = 0.50
Day 8 Ammo = 0.50 Nitrite = 2.00  added Ammonia up to 3 ppm
Day 10 - 17   Ammo = 2.00 Nit = 2.00
DAY 17 did 25% water change   
Day 17 - 20  Ammo = 1.00 Nit = 2.00
Day 20 did 50% water change Ammo = 0.50 Nit = 2.00 added Ammonia up to 3.ppm
Day 22 -26 Ammo = 2.00 Nitrate didn't test. Added 9ml of waterlife bacterlife
Day 27 Ammo = 2.00 Nitrite 2-6 ppm did 50% water change
Day 29 Ammo = 1.00  Nit =  2.00 Added old filter sponge from recently cycled tank
Day 31 -33 Ammo = 0.50  Nit = 2-5 ppm Added Ammo up to 2.0ppm

Day 34 Ammo = 0.50-1   Nit = 0.50
Day 35 Ammo = 1.00      Nit = 0.25
Day 37 Ammo = 1-2       Nit = 0         (first 0) Added Ammo up to 4 ppm
Day 38 Ammo = 1.00          Nit = 0      Nitrate = 20-40 ppm
Day 39 Ammo = 0.50 -1.00    Nit =  0 Added Ammonia up to 2.00 ppm
Day 40 Ammo = 2.00         Nit = 0
Day 41 Ammo = 1.00
Day 42 Ammo = 1.00 (still)
Day 43 Ammo =  0.50
Day 44 Ammo =  0.25    Nit = 0- 0.25  Did 90% WC
Day 45 Ammo = 0 Nit = 0   Bought two Platy's   (want to woo hoo! but not till i know if they survive)
Day 46 Ammo = 0 Nit =  0
Day 47 Ammo = 0 Nit = 0

Looking good!

Wait till you have had a week of double zeros, then you can get more fish. But no more than equal to one platy. You don't want to overwhelm those bacteria.

It doesn't matter how long you wait, you can still only add the same amount of fish. There are the exact number of bacteria in the tank to deal with the waste from the amount of fish in there now. The number of bacteria won't increase as long as the amount of fish stays the same; the bacteria will only grow in number if there is more food for them to eat. But it takes a while for them to catch up. So new fish have to be added a few at a time, and no more at any one addition than one third of the amount of fish in the tank now. They can multiply quickly enough to cope with an extra third of ammonia, and the nitrite made from that ammonia; but more than a third and it'll take longer for the bacteria to catch up.

You actually have more than 2 platies don't you? You have a guppy and perhaps an endler as well? A guppy + an endler = one platy, unless your platies are tiny babies. So you have three platy's-worth of fish, and a third of that is one platy. Or two endlers. That's all it's safe to add next. And you must check the ammonia and nitrite levels for several days after adding them.
Then when you've had a week of double zeros, you can add more fish. There will be more fish in the tank by then, so a third of them will be more than one platy's-worth.