Sudden rise in ammonia

So my tank has been up and running for almost a year now.. and i did not have any casualties.. yet the ammonia jumped from a consistent 0 for the past 8 months or so to 0.50... can't really find out the problem but the water is merky and my ph is also lowered to 7.8 from 8.3-4.. i'm doing a 25% water change, other than that, any other advice? No i have not added any live rock or sand or any livestock for that matter in the past 2 months at least

 

You could have had die off within the liver rock that will cause the spike. I had hitchiking crabs and worms that died in my LR that caused problems in my tank. It drove my nitrates into the 200+ppm range. I would imagine the same thing may have happened in your tank. I would just let it be. To do any real lowering of the toxins, you will have to do a serious volume of WC, about 75% or more. Doing a 25% WC will only lower your ammonia to .375.

 

I had the same thing happen... about 1 year later.. nothing died that i know of.. but suddenly my Ammonia went to .50 but funny thing is everything was normal.. Nitrate is at 5.0 .. phosphate is at 0 and my PH is at 8.4 the only thing that changed was that i bought a more powerful light... can that cause a spike? I had to use an Ammonia tablet to get rid of it..
Does anyone know if too much light may cause ammonia spike? it happend about two weeks after i installed my light.

 

very deep sand bed? heard something about this somewhere...