Very likely that the light is too old and failing; replace that with a proper bulb (depending on if you have plants or not. Get a 6700 K light for plants.) The nitrates are ok. The 10 ppm can lead to BGA but only if phosphates are rather high. Those require their own test kit which most don't care to get.

Try deeply stiring the sand when you vacuum and that should help lower the phosphates (these build up in sand very easily and are not easily removed by simple water changes.)