The nitrate level in my fish tank is too high. What can I do? I have done a 50% water change with treatment.?

1.

Nitrate levels are usually controlled with water changes, but stability in water chemistry is always more important than suddenly improving water quality.

2

Don't do larger water changes. Just do proper maintenance more often until the condition improves.

3

Feed less if you are overfeeding. There should never be uneaten food in your tank even minutes after feeding.

4

Use your siphon gravel vacuum gently to remove more filth and less water, do not stir up the gravel unnecessarily.

5

If you don't have one, get it.

6

!!!!!!!! Never clean or replace all of the filter materials at once !!!!!!. Rinse them in dirty tank water you take out for a water change if possible, rather than tap water.

7

Don't use ammonia removing filter materials (often look like white rocks)

8

Replace only carbon filter material (I rarely use carbon at all, and always remove it within weeks), most other filter materials shouldn't or don't need to be replaced.

For your current issue, if Nitrates are below 50 ppm, continue with slightly increased frequency of normal 25% approx. water changes and follow instructions above. If higher than 50 ppm, you may need to evaluate your situation and do 20-30% water changes every few days or weekly if you are very careful about temperature and using an excellent water conditioner and aerating the new water before using.

If this is a live planted tank, then reduce your feeding to near zero , discontinue fertilizing until the problem is solved, and evaluate your fish load, feeding habits, fertilizing .

Without proper lighting etc. a planted tank will go foul and won't have good plant growth, contributing to nitrate rather than reducing it.

Regular water changes are your best option. Nitrate is the end product in the nitrogen cycle so it doesn't indicate incomplete cycling.