I just did a test and did a water change yesterday, the test today showed 0 ammonia, 7.6 ph, 0 nitrate and big spike in nitrite around 5. Should i do another water change to reduce that nitrite. BTW i dont know why my nitrate keeps showing 0 either, my tank is 3.5 gallon and its filtered and heatered.
Yep definitely needs another change. Nitrite is the worst one and stops the blood from being able to take up oxygen. It can do permanent damage if hes exposed to it for too long. Do 80% change and test again, you need 0 nitrite. Do you have prime? If so put that in and it will detoxify nitrite for a day, then do another 50% the next day, test water again, if you still have nitrite, add prime, 50% next day etc
How long has the tank been set up for?
Also test your tap water, make sure its not your tap water thats messing it up, if its not your tap water then the fact that you have 0 ammonia, high nitrites and 0 nitrates means your tank hasnt finished cycling, its about halfway through.
When cycling your tank will go through an ammonia spike (from the fish waste or whatever ammonia source you use)
Then the ammonia will go down as bacteria eat it up
Those bacteria that eat ammonia produce nitrite as a byproduct,so you see the nitrite will go up
Then another species of bacteria comes into play and eats up the nitrite and turns it into nitrate which is safe at low levels
So a fully cycled tank will have 0 ammonia, 0 nitrite and some nitrate.
Then when you do your water changes you are taking out the nitrate.
The high spikes that go on while a tank is cycling is why its not recommended to cycle with a live fish, unless you are prepared for constant monitoring of the tank parameters and regular big waterchanges to ensure the toxins stay at at safe level
Salt can be used to prevent nitrite poisoning, the chloride ions must be 30 times the concentration of nitrite ions. Nitrite reaches a toxic level at about 0.1 ppm, which requires 3 ppm of chloride ions, half a teaspoon of salt would be more than enough in a 3.5 g tank.
1 teaspoon of salt would treat 100 gallons of water at the above ratio.
Good that you got the nitrite under control
Id keep testing the water every few days to keep up track of the cycle, its almost finished, just need those nitrites to go down and nitrates to go up. IME the cycle usually takes ~ 4 weeks, but it can be less or more, theres no set time limit on it
ok the other thing im concerned about is the substrate i have never cleaned them, as in take them out and wash them and then put it back in, do they need to be cleaned?? because i dont have anything to clean that with. i know that good bacteria is under there but just worried bout when it actually needs to be cleaned before it does damage.
Nah you dont need to rinse out the gravel, just do a gravel vac which will suck up all the poo thats hiding in there. They are pretty cheap to buy and theres quite a few tutorials on YouTube if you cant get it going
i have never cleaned them, as in take them out and wash them and then put it back in
You NEVER EVER do that no matter what others say.
The greatest population of bacteria in a healthy balanced aquarium occurs in the substrate, not the filter. The floc or humic compost that collects in the substrate is the host for the biofilms; this is why the substrate in planted tanks should never be disturbed, and many aquarists apply this to non-planted tanks as well.
In very general terms, aerobic nitrification takes place in the top 1-2 inches of the substrate; anaerobic de-nitrification takes place approximately 2-4 inches down, and anaerobic bacteria producing hydrogen sulfide occurs in substrates deeper than 3-4 inches. In all three cases, it will be deeper in coarse substrates (like pea gravel) and more shallow in finer substrates such as sand. These generalities will also vary with the presence of live plant roots and substrate “diggers” such as snails and worms, since these factors result in more oxygen being made available in the substrate, reducing anaerobic bacteria activity. An oxygen level in the substrate of as little as 1 ppm promotes nitrogen reduction rather than sulfur reduction (hydrogen sulfide). 
Maintaining a substrate of fine gravel or sand no deeper than 4 inches, having live plants rooted in the substrate, and keeping Malaysian Livebearing snails are the best and safest methods of providing a healthy biological system for aerobic and denitrifying anaerobic bacteria.
+1 Nick, for some reason so many people seem to think nothing lives in the substrate and that it needs to be completely cleaned. Substrate and filter media are the two main homes of your bacteria, its best not to mess around with them