High nitrites may cause pH to lower but likely won't be the sole cause, low kH may be a factor in this, if its low kH then adding some inorganic carbon will help to buffer this (kH level will make the pH unsteady if below 55ppm).
Without further evidence of this, as op says their pH is at 8 which is actually a good level for cycling to be fair, would not suggest altering kH or pH at all at this stage.
Anyhow, doing a water change will help to lower nitrite levels if they are at a dangerous levels for the cycling process. I would suggest if nitrite is at 14+ ppm then thats time to do a partial 30-50% water change to bring nitrite level back down to 5-10ppm.
Do keep an eye on your ammonia dosages as 3ppm at the correct intervals helps to keep nitrite levels at a good level, adding too much ammonia too soon at the wrong stage may means the Nitrosomonas (ammonia eating bacteria) will produce too much nitrite and if there is not enough Nitrobacter (nitrite eating bacteria) will then not be able to cope with the high nitrite numbers and thus stalls the cycle.
Anyhow, if nitrite continues to be at 2-5ppm, then the suggestions of adding live plants and/or a decent handful of substrate from an established tank is a good idea as this will likely contain both the Nitrosomas and Nitrobacter bacteriums that will quickly colonise in your tank and help to deal with both ammonia and nitrites at a faster rate.
Most tank cycles can take up to (and sometimes more than) 40 days to fully successfully cycle so do not worry too much if it appears to be taking its time before seeing any drops in nitrite numbers.
Patience is key
