What level should nitrate number 3 be for salt water fish?

There seems to be a misunderstanding in your question. There's no such thing as "nitrate number 3."

Nitrates are a common byproduct of the nitrogen cycle in aquariums, and they can be harmful to fish in high concentrations.

Here's what you need to know about nitrates in saltwater aquariums:

* Ideal Nitrate Levels: For saltwater fish, the ideal nitrate level is below 5 ppm (parts per million). Some fish can tolerate higher levels, but it's generally best to keep them as low as possible.

* Harmful Levels: Levels above 20 ppm can become toxic to many saltwater fish, and levels above 50 ppm are extremely harmful.

* Testing for Nitrates: You can test for nitrates using a water test kit specifically designed for saltwater aquariums.

* Reducing Nitrate Levels: Several methods can help reduce nitrate levels in saltwater aquariums, including:

* Regular water changes: The most effective method is to perform partial water changes regularly (10-20% per week).

* Proper filtration: A good filter system helps remove nitrates.

* Skimmers: Protein skimmers remove organic matter that contributes to nitrate buildup.

* Live rock and coral: These can help reduce nitrates naturally.

Remember: Always consult with your veterinarian or a qualified aquarist for advice specific to your fish and aquarium setup.