Before testing of Nitrite level, Here is some point and guideline,  what you need to do. : 1 take the following readings; pH, TDS (uS), and nitrite level.and record. 2 add the Chemical your are using. 3. wait for a period of time for the sysem to circulate. hours> 4. Re check the readings. and record. 5 track these readings
for a period of time.

If the TDS and Nitrite drop you have a leak/ unknown makeup. if the TDS stays stable and the nitrite drops you have a biological problem. Bacteria that convert nitrite to nitrate.

Solution ::: Use DI water in place of general water, And also use. Algaecide to control Bacterial growth inside water system ... http://rxmarine.com/Biocide-Algaecide

Advanced formulatory High performance Corrosion Inhibitor,  nitrite  borate based  with antifungal Azole and alkalinity indicator for closed chilled system.

Avoid any contact with DRINKING water.

Use proper chemical protective hand gloves and Eye Goggles.

Corrosion inhibitor closed cooling systems Molybdate Phosphonate is very effective in high hardness, highly alkaline scaling waters. It contains a proprietary blend of organic and polymeric sequestrants, penetrants and dispersants to minimize system fouling from contaminants such as calcium, silica, iron, sludge and organics. It also contains a unique blend of organic and actives to corrosion sites. Corrosion inhibitor closed cooling systems Molybdate Phosphonate is very effective also in low hardness, low alkalinity corrosive waters. It contains special filming ingredients to establish protective barriers against corrosion on ferrous metal surfaces. It also contains special filming ingredients to establish a protective barrier against corrosion and pitting on both yellow metal and ferrous metal surfaces.

Corrosion inhibitor closed cooling systems Molybdate Phosphonate is environmentally safe for discharge with the cooling system bleedoff. The formulation contains no heavy metals, chromates, or other pollutants requiring removal or treatment prior to discharge at normal usage rates.

Molybdate does not provide a nutrient source as do many other corrosion inhibitors. This eliminates a food source for algae and bacteria in the water system and makes control of microorganisms easier at lower microbiocide dosage rates. Corrosion inhibitor closed cooling systems Molybdate Phosphonate may be used alone as a single product for control of corrosion in systems where hardness and alkalinity does not pose a scaling problem, or in high hardness and/or high alkalinity waters where higher cycles of concentration and lower bleed rates are desired. Corrosion inhibitor closed cooling systems Molybdate Phosphonate offers superior corrosion protection for all metals typically found in cooling water systems. The blend of cathodic and anodic inhibitors provides a durable corrosion inhibitive film for maximum system protection and minimal corrosion rates.

Scale inhibitor for fresh water generators and desalination plants.

Features of Corrosion Scale Inhibitor which can be used for both Open and Closed Cooling Systems

• Corrosion Scale Inhibitor for Open Closed Cooling systems ECO is a very efficient dispersant for hardness-salts and metallic-oxides.

• Corrosion Scale Inhibitor for Open Closed Cooling systems ECO is also a very efficient corrosion-inhibitor.

• Corrosion Scale Inhibitor for Open Closed Cooling systems ECO contains sequestrants, anionic polymers and wetting-agents.

• Corrosion Scale Inhibitor for Open Closed Cooling systems ECO has been developed to avoid or remove deposits composed of calcium carbonate, calcium sulphate, magnesium hydroxide, iron oxide, insoluble phosphates and silicates.

• Corrosion Scale Inhibitor for Open Closed Cooling systems ECO may be applied in closed, open and once-through cooling-water systems, desalinisation plants, phosphoric acid plant and all other systems where above mentioned deposits will occur.