This is a 4 part series where our host, Matthew, tackles aquarium water testing. Water parameters are certainly the most complicated aspect of maintaining a healthy aquarium, it can be overwhelming or intimidating for new hobbyists. Knowing what to test for, when to test, and what to do with that information is all very important to your success.

A wise hobbyist once said, "We maintain and keep the water, the animals just live there" which means if you focus on keeping healthy and stable water quality, the fish and other animals take care of themselves outside of regular feeding.  When it comes down to it, almost everything you do for the aquarium is designed to keep the water quality in a condition that is safe for the fish and other inhabitants. Without testing, you can never be certain your doing that successfully.

The Nitrogen Cycle

The nitrogen cycle is the biological process that happens in your tank that handles waste; decaying organic matter & fish waste specifically. It makes the water safe for your fish. When you "cycle" your tank, you are establishing the bacteria necessary to sustain a nitrogen cycle in your tank.

The compounds that are created by the nitrogen cycle are the first water testing you're going to encounter outside of basic parameters like temperature and pH.  

Aquarium Cycle Nitrogen Cycle

Ammonia, Nitrite, and Nitrate

  • NH3 - Ammonia: Deadly toxic to your fish.
  • NO2- Nitrite: Still toxic, just not as deadly as ammonia.
  • NO3- Nitrate: Only toxic at very high concentrations.

During a cycle, you are testing these three parameters to monitor the nitrogen cycle and ensure it has been established in order to know when it is safe to add fish.

While you are stocking the tank, you are testing in order to ensure toxic ammonia and nitrite do not show up and kill your fish - sometimes we call this the secondary cycle because the bacteria need to grow and accommodate the new waste that comes with new fish. Monitoring that "secondary cycle" that is occurring is important to ensure your tank's biological filter is developing but also to ensure you're not adding too many fish.  

Once the tank is well established and you are not adding new fish, you monitor nitrate only on a weekly basis to ensure excessive waste is not being built up in the aquarium. Should you end up with rising nitrate, you must remedy the situation before water quality begins to suffer and nuisance algae become a threat.  

Learn More With BRStv:

Ammonia Control

Ammonia is the most toxic of the compounds that can occur as a result of fish waste and the nitrogen cycle. Should you experience rising ammonia in your aquarium while adding fish, your biological filter is not sufficient for the bioload (amount of fish) you have. Sometimes it's just a result of adding fish too quickly, sometimes your overfeeding, sometimes your biofilter is just not yet established enough to handle the bioload. The best approach is often a combination of solutions to ultimately create a stable aquarium.

How To Reduce Ammonia Levels:

  • Perform frequent water changes until the biofilter can catch up
  • Reduce bioload by removing fish or reducing feeding
  • Improve filtration capacity/efficacy
  • Add more biofiltration

**Pro Tip - Perform daily ammonia and nitrite testing while cycling the aquarium and when adding fish. You also don't need an expensive ammonia test kit to get the job done, the API Master Saltwater Test Kit is great for beginners, or consider the Seachem Ammonia Alert which is a constant in-tank ammonia monitor. 

Nitrate & Phosphate

These are the two parameters you will end up testing for most often after the tank is cycled and stocked with fish.  These are the indicator parameters of the water quality in your aquarium and the key to good water quality is keeping them in balance, not too high but not too low either. You should be testing for nitrate and phosphate at least once each week. 

  • Recommended Nitrate Levels: 1-10 ppm
  • Recommended Phosphate Levels: 0.01 - 0.03 ppm

View Reef Tank Parameters Chart

We already talked about nitrate which is the result of organic waste and uneaten fish food being broken down in your aquarium by bacteria (nitrogen cycle). Phosphate is simply another byproduct of the nitrogen cycle process; most anything that winds up as nitrate in the aquarium water will also contain some level of phosphorous as well.

While nitrates and phosphates are not directly toxic to tank inhabitants, they can lead to some pesky problems if not maintained at the proper levels. Most importantly, they can be direct fuel for nuisance algae growth; fertilizer for algae is a good way to explain it. Phosphate specifically can also inhibit calcification among your corals if left to compound in the aquarium water. On the other hand, if nitrate and phosphate are too low, you end up starving out the corals and some of the beneficial bacteria in your aquarium. This often allows for pests like cyanobacteria and dinoflagellates to grow and begin to dominate the biome. 

Nitrate and Phosphate Control

By removing waste and uneaten food before it is broken down into nitrate and phosphate, you can effectively prevent the build-up of excess nitrate and phosphate. Most all of your regular filtration and maintenance are designed to export waste that creates nitrate and phosphate.

  • protein skimmers
  • mechanical filtration
  • organic waste removal media
  • siphoning out debris during water changes/cleaning the sand 

Once the waste is processed through the nitrogen cycle, you now are dealing with the Nitrate and phosphate directly which are dissolved organic compounds and need to be removed a little differently. 

  • water changes
  • macroalgae
  • algae scrubbers
  • biopellets
  • anaerobic biofiltration
  • carbon dosing

Should you encounter excess nitrate and phosphates, it simply means you have too much fish food going into the aquarium, resulting in too much waste in the aquarium. The remedy the situation you should first work to immediately lower the dissolved nitrate and phosphate levels using direct removal techniques. Once your testing nitrate and phosphate to be within the ideal range, you need to establish a longer-lasting solution that removes the leftover food/waste more efficiently which is done via improved filtration and/or maintenance.

**Pro-tip: Pellet food is 5x - 10x more nutrient-dense compared to frozen foods meaning your 5x-10x more likely to overfeed. Sometimes all it takes is changing up your feeding habits to get your rising nitrate and phosphate under control. Another reason you might see a nitrate/phosphate spike is if something dies unexpectedly and the carcass is left to break down inside the aquarium.  

Nuisance Algae - Too Much NO3 and PO4

Nuisance algae use light, nitrate, and phosphate to grow inside your aquarium. When nitrates and phosphate are left to rise, nuisance algae grows and absorbs nitrate and phosphate in the process. This can lead to a false sense of security, so to speak, because you might be testing with acceptable levels of nitrate and phosphate but still experience nuisance algae growth. This is because the algae are using that nitrate and phosphate instead of it being exported from your aquarium.  

In this case, you need to improve the methods of removing leftover food and fish waste before it can be turned into nitrate and phosphate combined with the physical removal of the nuisance algae. Nuisance algae take up nitrate and phosphate very quickly in the aquarium because they grow quickly.  The longer you wait to address the problem, the longer it takes to overcome it. 

Cyanobacteria and Dinoflagellates - Zero NO3 and PO4

These pests are often encountered when the aquarium is too clean. When nitrate and phosphate are essentially so low, they are undetectable by your test kits. We often call it the "double zero" effect which allows pest organisms to begin to dominate the biome.  In these cases, sometimes all it takes is for you to increase nitrates and phosphates in the water.

Method Of Increasing Nitrate and Phosphate:

  • Increase feeding amount/frequency
  • Turn off protein skimmer
  • Remove filter sock or other mechanical filters
  • Reduce water changes
  • Dose nitrate and phosphate additives
  • Reduce the growth in your refugium or turf algae scrubber

In many cases, a little more food will do the trick but sometimes you also have to reduce the filtration capacity.  Should you encounter cyano or dinos, it is also important to physically remove the pest themselves on a very regular basis via a siphon while also maintaining the proper balance of nitrate and phosphate. 

High Nitrate NO3 & Low Phosphate PO4

When a tank is new, it is not uncommon to be dealing with elevated nitrates. While nitrate naturally stacks up in any aquarium, mature aquariums tend to do a better job of handling the nitrate directly via anaerobic bacteria. Anerobic bacteria is a type of beneficial bacteria that actually processes nitrate into nitrogen gas, effectively eliminating the nitrate from your aquarium water.  This bacteria seems to take much longer to establish in the aquarium and also is limited in terms of the areas it can survive.

Anaerobic bacteria only survive in oxygen-depleted environments; that would be deep in your sand bed below the first 2" or deep within your porous live rock. These oxygen-depleted areas are just limited in an aquarium which is exactly why we must perform water changes and employ filtration techniques like a refugium, protein skimmer, etc.... to help us reduce the threat of rising nitrate.  As your aquarium matures, these anaerobic bacteria become more capable or abundant which means your tank will better be able to take care of some nitrate all by itself, in the meantime, it's up to you to export those nutrients and resulting nitrate via maintenance and filtration. 

  • Nitrate is not directly toxic but can be problematic at extremely high levels beyond 30 ppm
  • Less than 20 ppm Nitrate is generally safe for most aquariums..

Sudden Rise In Nitrate NO3 & Phosphate PO4

In some situations, you might experience a seemingly random rise in nutrient levels. The most common reason this happens is when something has unexpectedly died in the aquarium and the carcass is left to decay in the water. If you should experience a sudden rise in nitrate and phosphate, scour the aquarium and be sure to remove any dead animals. Examine and maintain your filtration carefully, perform a water change, and adjust the filtration as necessary to handle the nutrient load. 

Nitrate & Phosphate Testing Tips

  • Having test kits for nutrients is a fundamental part of controlling nitrate and phosphate. The Hanna Instruments High Range Nitrate and Low Range Phosphate Checkers are easy to use and provide consistent results. Just be sure to keep plenty of reagents on hand at all times. 
  • Test nitrate and phosphate twice weekly for at least the first 3-6 months while you get accustomed to managing nutrient levels. Past that, once weekly should suffice.
  • Always keep a logbook to record your test results. 
  • Take action immediately if you see rising or depleted nitrate and/or phosphate levels in your aquarium, do not neglect it. 
  • Don't overcompensate, especially when it comes to the use of GFO and phosphate control.

Calcium, Alkalinity, Magnesium & pH

These are the first parameters you will need to manage in order to successfully keep corals and other sessile invertebrates in your aquarium. The big difference in caring for a saltwater fish-only aquarium and a reef tank is the monitoring and control of these major elements in the aquarium water. While these may not be of immediate concern to you as a beginner, they should be on your radar if you want to eventually keep corals.  

  • Acceptable Calcium range: 380 - 450 ppm
  • Acceptable Alkalinity range: 8 -12 dKH
  • Acceptable Magnesium range: 1200-1400 ppm
  • Acceptable pH range: 7.8 - 8.3 is acceptable but work to maintain it as close to 8.3 as you possibly can.

The trick with successful calcium and alkalinity levels is stability. Just because your levels test within the outlined range, that doesn't mean you are keeping things stable. Choose a number and stick to it; don't go chasing numbers and allowing the levels to fluctuate within the target zone.

Your salt mix has a lot to do with creating the baseline parameters in your tank because that is your starting point with each water change. Check and verify the parameters of your freshly mixed saltwater before it goes into your aquarium, your target levels should not be too far from those parameters.  Here are the BRS Recommended reef tank parameters. 

  • Ideal Calcium level: 440 ppm
  • Ideal Alkalinity level: 9 dKH
  • Ideal Magnesium level: 1350 ppm
  • Ideal pH level: As close to 8.3 as you possibly can.

Learn More With BRStv: A Beginner's Guide to Calcium and Alkalinity - The Cool Part Of Reefkeeping

Low Calcium and Alkalinity

If you run into low levels of calcium and/or alkalinity you're going to inhibit the growth of stony corals. That includes both your SPS and LPS corals; any coral that deposits a hard skeleton onto the reef rock. This happens because the rate at which your corals are consuming the major elements has overcome your daily addition of calcium and alkalinity additives. To correct the issue, you can adjust the tank using additives directly but water changes are often an easier approach. 

  1. Begin to test parameters daily
  2. Perform a series of partial water changes every other day until you reach your target parameters. 
  3. Adjust daily addition of calcium and alkalinity additives to meet your tank's demand. 

Elevated Calcium and Alkalinity

Elevated calcium and alkalinity levels typically happen when you add too much of your additives.  Whether that was a single accidental overdose or a slow creep over time with your daily dose, the levels need to be corrected.  Elevated calcium and alkalinity levels can stress out corals to a point at which they will stop growing and also put you at risk of a precipitation event. 

The good news, you can just stop dosing calcium and alkalinity additives and the levels will naturally come down. You can also just do a series of water changes if you find yourself drastically over the target levels. Once you're back on target, re-adjust your daily dosing amount to meet your tank's demand. Remember your levels climbed up for a reason, so you must adjust the amount of additive you use on a daily basis to get back on track moving forward.  

Calcium and Alkalinity Out Of Balance

Maintaining the perfect ratio of calcium to alkalinity is important. If one of the two rises and the other falls, you must get back in the balance right away. It might be calcium is high and alkalinity is low, or vice versa. Regardless, just perform a series of water changes to get back on track.  Avoid the urge to try and use additives to adjust your levels as a beginner because water changes are simply much easier and will correct both parameters together. 

After you are back in balance, readjust your daily dosing to meet your tank's demand.  

Low pH

PH is affected by a variety of factors in your aquarium. Most notably the amount of CO2 and alkalinity levels. Low alkalinity and too much dissolved CO2 always cause low pH. Should you experience low pH levels, here is what you can do. 

  • Verify you're maintaining the proper stable alkalinity level in your aquarium
  • Open a window to allow for better air exchange around the tank

If you cannot seem to get the pH above 8.0, it's not going to kill your tank. It just means there is too much CO2 being dissolved into the water and your corals will just grow a little slower. As long as you keep the pH above 7.8, the tank will be safe.  Shoot for 8.3 but if it just doesn't work out, don't fret and just focus on stability among your calcium, alkalinity, and magnesium. 

Can't Raise dKH

Related to the above low pH, sometimes you just can't get your dKH above 8.0. While we tell you to shoot for 9.0 dKH, anything above 7 is safe. In cases where elevated CO2 is a problem and pH is low, dKH can be difficult to raise.  So if this is your tank, just keep that alkalinity within the  7 - 8 dKH range and be sure that pH is above 7.8 pH at all times.  If you fall out of range, immediately do some water changes and be sure a window is open to get the tank back in balance. 

Ca, dKH, Mg, and pH Testing Tips