pH, Nitrite and Nitrate - Ideal levels

pH will tend to drift down over time in a well balanced system and will need to be buffered up from time to time.

In a new system that is in the process of being cycled it is not uncommon to experience swings in pH. The type of media used can have a bearing on pH. For example, some gravels can be high in natural lime or similar akaline elements. This situation could make it difficult or even impossible to keep the pH at 7.0 or just below 7.0

In a system that has completed cycling, Ammonia should be very low, only barely detectable, sometimes not detectable at all.

If the good bacteria are present and in sufficent concentrations, and there is sufficent water movement, the Ammonia will be processed very quickly.

Nitrite will be seen when the system is part way through the cycling process and not be seen in a balanced system. As the system is cycling Ammonia will first be detected, several days later Nitrite will be detected. Then finally Nitrates will be seen.

Nitrates can be moderate to high without harming the fish. Nitrates should not be high permanently. If they are consistently high, plant more grow beds out to use up the nitrates, or reduce feeding of the fish.

If Nitrates are very high over a long period of time fish health will be diminished.

Posted By Murray Hallam on Monday 12th December 2011 @ 06:15:02

Updated : Friday 4th October 2013 @ 03:09:22 | Words : 230 | Views : 2505 | Comments : 20


RSS Twitter Facebook



Hi Murray I have noticed that me Nitrate levels have dropped over the last month or so in both my separate systems and as a consequence ammonia level in one systems increased marginally (still very low) there is no apparent blockage and Autosyphons both working fine, this is my first winter, is this normal as the temperature has been down a bit (hovering around the 18 degree mark) does the bacteria colonies die off a bit in winter? Systems are still quite immature about 7 months old.

Posted By Jeff Palmer on Thursday 15th August 2013 @ 08:34:34


Hi Jeff,
Beneficial bacteria activity drops off as temp lowers. Is 18 deg the water temp? It will pick up now spring is upon us.

Posted By Murray on Thursday 15th August 2013 @ 08:34:34


Yes 18 degrees has been the average water temp for the last few months (here on the Gold Coast Qld) I do have water heaters in over night if the temp gets really low which manages to maintain that 18.


Posted By Jeff Palmer on Thursday 15th August 2013 @ 08:34:34


Hi Jeff,
Our water temps are lower than that. Generally speaking it is best to keep the fish at 15 c and above although some species such as Silver Perch and Murray Cod can deal with lower temps.

Posted By Murray on Thursday 15th August 2013 @ 08:34:34


Hi Murray

How do you reduce the amount of phosphate in a system. The system is new (8 weeks) and has cycled (.25ppm amonia and .25ppm nitrite). I have had levels up to 10ppm and have dumped 50% water for the last week and it is now sitting around 2ppm. Is this the only way?



Posted By Michael McRostie on Monday 12th August 2013 @ 12:09:11


Hi Michael,
Sorry, I don't know the answer to that, never had the problem. Where are the phosphates coming from?

Posted By Murray on Monday 12th August 2013 @ 12:09:11


G'day Murry,
Mate got a bit of a problem with high nitrites, i have a new system i built myself prob about 7 weeks old i have plants and fish. Getting good growth. I have very low ammonia levels, high nitrite which doesnt seem to going up or down staying around 5 ppm, and varying nitrate levels which is fine for me at the moment 40 - 120 ppm. I have tried water changes and not feeding for a few days, water changed helped at the time but now its back up 3 days later. The system is an ibc system 650L tank with 16 silver perch and the top is 300mm deep with expanded clay..
Any ideas mate would be great.

Posted By Nathan Haines on Monday 6th May 2013 @ 07:23:08


Hi Nathan, What are you using to test the water? Are you following the test instructions carefully? Your NITRITE should disappear in a few days. By your readings you are almost through the cycling process. Be careful of the NITRITES, the should be dropping right out very soon

Posted By Murray on Monday 6th May 2013 @ 07:23:08


Hello Mr Halam, Sorry for asking this question here but I need help. I have one grow bed and one fish tank and a sump. I want to set up a new set of 2 grow beds and one fish tank without using a sump. How do I connect the inlets to 2 grow beds from the fish tank please? I have adequate water in the fish tank as its rather large. Roughly, 1K litres I think.Thank you, Annie

Posted By Annie Low on Thursday 31st May 2012 @ 12:24:49


I have an AP system made from a 1000 liter tote, (I'm a missionary in Mexico) I used volcanic rock and did my best to sift it to 20mm gravel bits, however there are a few smaller pieces in there. in it I have about 15 tilapia or so and a chili bush in the grow bed until my seeds have sprouted and my other plants are ready. I started the system about two months ago and my pH is still up around 7.8 or 8.0, I have well water and I use vinegar to bring the pH down, however it wont stay down, I did tests on the lava rock prior and found that it was pH neutral, the system seems to have cycled and has been turning the ammonia into nitrates for some time now, does anybody have any idea what I'm doing wrong regarding the high pH, I can't keep it down? I've added some red worms and gammarus to the system to help break down the matter that is caught in the grow beds.
I've been super excited to start ever since I purchased your dvd's, please help me use this for our community here.

Posted By Josua Angel on Tuesday 22nd May 2012 @ 20:54:39


Just let it settle for a while. If it stays up there look for something that is kicking it up. Do you have concrete tanks?

Posted By Murray on Tuesday 22nd May 2012 @ 20:54:39


how much longer should I let it settle for? the tanks that I have are the plastic 1000 liter totes, would concrete increase the ph? I have a local person in the village that is considering building a system from concrete. Also, a few days ago the siphon wasn't working propperly and the flow was to much, so for about a day (maybe two) the siphon kept the flow going, I was out of town. on my return I noticed the problem and fixed it right away, however a handfull of fish died, I'm wondering if the bacteria suffered loss and if this somehow is a consequence.

Posted By Josua Angel on Tuesday 22nd May 2012 @ 20:54:39


the siphon problem wasn't allowing the gravel grow bed to fill and drain, which is why I thought the fish died off (they're getting up around 200-300 grams), if you think that didn't cause the die off then I'm wondering what did. I have made sure that there are no lime containing stone in my media, I'm a digital ph Meter and the API master test kits for the ammonia, nitrite and nitrate tests and I'm using them as directed on the instructions (waiting for the alloted time for the results).....the pH of my top off water is at 8.0 but as much as I try to bring it down it keeps coming back.
By the way, thank you so much for your patience with helping in these issues.

Posted By Josua Angel on Tuesday 22nd May 2012 @ 20:54:39


Mr Murray
how long does it usually take a system to balance its pH after its cycled its ammonias into nitrates?

Posted By Josua Angel on Tuesday 22nd May 2012 @ 20:54:39


my climate here is warm year round, almost like hawaii

Posted By Josua Angel on Tuesday 22nd May 2012 @ 20:54:39


Hi AP community. I have just gotten started in my AP system. It is now almost 5 weeks old, my plants are thriving and my beans already have flowers. My pH is about 6.8 and my ammonia is undetectable, however, my NO2 and NO3 are both high. I just added 11 juvenile Tilapia to my 120 l tank. The NO2 and NO3 levels were high before the addition. I have changed out 100% of my water over the last 24 hours, and the levels are still high. I have concluded that I must have a build up of fish waste/uneaten food in my grow bed that is causing the high readings...any thoughts?? Yesterday I added some compost worms to the mix in hopes that they will help to bring down these levels. Any advice would be appreciated!

Posted By Troy Bingham on Friday 9th March 2012 @ 20:36:38


Hi Troy,
Nitrite NO2 is not good for your fish. In fact it is more of a worry that high ammonia levels. It should rapidly disappear if there is actually Nitrate NO3 appearing in your system. Make sure you are doing your tests strictly as per directions and invest in a master test kit. Strip type tests are usually poor quality.

Posted By Murray on Friday 9th March 2012 @ 20:36:38


I have been struggling with my Ph for some time now... My system has been set up for a while and I have a few issues. The ph has been somewhere between 7.6-8.2 since i set it up approx. 5-6 months ago. I have tried so many things to lower the ph but whatever I do even if it reads lowered after a few hours it will be back to high the next day. I have nearly 100 gallons in the system at any one time. cycling through a 4' square bed that is 11" deep. I have a floating raft that is also 11" deep but nothing will grow in it currently due to the high Ph and also it might have something to do with a lack of a sediment filter.

I have added 500mL of 5% HCl, 1 liter of pure citric acid crystals, a few liters of lemon juice, gallon of vinegar, liter of organic ph down which i believe was mostly citric acid. and the juice of many lemons. So far i have had no luck. My water is pretty hard to begin with and my nitrates and ammonia are reading nearly zero. I know that I need more fish, which i plan to get this week but my plants are "growing" even if very slowly. Also to note this system is an indoor running under a 400W t-5 fluoroscent 8-bulb light.

Any tips would be extremely appreciated, and especially if you have experience running a system off artificual light.

Thanks from Montana USA

Posted By Brandon Wasser on Thursday 16th February 2012 @ 01:32:50


Hi Brandon,
There must be something driving up the pH in your system. The input (top up) water might be the culprit or the media you are using. Some gravel is high in limestone and that may be your problem. It can take some time to move the pH down, but after 6 months I would have expected to see some movement by now. Using Hydrochloric acid is the best way and not at all expensive. Using lemon juice and the like is expensive. The sediment filter or lack of will have nothing to do with your current dilemma. Try again using the hydrochloric acid. Add some every day, about three tablespoons and watch the movement. If it keeps bouncing back up, there must be some other factor like limestone in your gravel that is pushing the pH up all the time.

Posted By Murray on Thursday 16th February 2012 @ 01:32:50

Post Comment

Please complete the following form to add a comment to the "pH, Nitrite and Nitrate - Ideal levels" Blog:

Comment Information

(This is the name that will display online)

Display Please email me when somebody posts a comment about this Blog.


Please do not enter your email or phone number in the "Message" box. Enter in designated boxes above.

Enter this Code *
Please enter Security Code to continue (Case Sensitive)

Login to the Blog OR Register FREE

Username or Email Address


Remember Me

Is the Pipe Poisonous?

Many ask the question about PVC pipe, should I use it in my home or commercial project. Most folk us . . .

Posted By Murray Hallam on Friday 31st July 2015

Words : 429 | Views : 2732 | Comments : 21

Tech Talk Introduction Video

Tech Talk Introduction video. Secrets1 from Murray Hallam on Vimeo. Join now to see Tech Talk vi . . .

Posted By Murray Hallam on Monday 18th May 2015

Words : 29 | Views : 2375 | Comments : 0

Tech Talk Video Collection

Cotton Wool Disease in fish. Secrets from Murray Hallam on Vimeo. I want to start a farm. S . . .

Posted By Murray Hallam on Monday 18th May 2015

Words : 127 | Views : 2323 | Comments : 10

Blogger : Practical Aquaponics

Practical Aquaponics . . .

Registered Since Monday 30th November -0001

Topics : 91 | Comments : 702

Share with Us


Additional Information


Murray Hallam is probably the best-known face in the world-wide Aquaponics movement. Murray is by nature an innovator and in his Research & Development facility has perfected many new methodologies for commercial farm Aquaponic systems.


Learn Aquaponics

At Practical Aquaponics, we have a range of information suitable for the novice to the expert. Browse our blog, register for our Aquaponics Courses, Workshops and Seminars or buy kits, books, DVDs and many other aquaponics necessities in our shop.


Aquaponics Kits & DIY

Proven and tested, there are hundreds of our kits in operation in every state of Australia and we have exported our kits to the USA, Hong Kong, New Zealand and Nassau. The wonderful thing about Aquaponics is that almost anyone can participate and get to grow some clean, healthy vegetables and fish.



Everything you could possibly need to set up an Aquaponics farm or home system is found in our online store. Whether you are looking to do Aquaponics in Brisbane, Perth, or anywhere in between, we’ve got you covered with the best range of products Australia-wide.


Featured Products

Indy 23 System - Plans And Building Instructions

Indy 23 System - Plans And Building Instructions

The Indy 23 Aquaponic System Can Provide A Family Of Four With All The Vegetables Needed, Year-round, With Proper Management. This Plan Set Covers Eve ...

from $395.00 buy online

Greenhouse Tours 2020

Greenhouse Tours 2020

Join Us For An Insightful One-hour Tour Of Our Aquaponics Facility. Get An Overview Of How Aquaponics Works. See Different Types And Sizes Of Systems. ...

from $20.00 buy online

Consultation Or Tour With Murray

Consultation Or Tour With Murray

If You Would Specifically Like To Have Murray Host Your Private One-hour Greenhouse Tour (rather Than Another Knowledgeable Staff Member) Or Arrange A ...

from $170.00 buy online

Call our team today on 07 3200 0272

For all things Aquaponics ... Practical Aquaponics is your number #1 choice for products and information. Give us a call or drop us an email about your farm project today.