Fishless Cycle Nitrate Drop

Hello,

Looking for some input on why I might be seeing a decrease in nitrates during my fishless cycle.

Tank Parameters

• 75 gallon filled with dechlorinated tap water
• pH started around 7.2 and has stabilized over the course of cycling at 7.0
• Water temperature is set to 79.5 F
• Fluval 407 Canister filter, using provided Bio-Max rings in one tray, as well as 200 g Seachem Matrix in a second tray

Cycling Data

• I initially dosed Fritz Pro Ammonium chloride to 4 ppm on Day 0.
• I started seeing nitrites on Day 2 and nitrates on Day 4.
• On Day 7 ammonia dropped to 1 ppm. I dosed additional ammonium chloride back to 3 ppm.
• 24 hours later on Day 8 the ammonia is back down to zero. The nitrite has also decreased down to 1 ppm. I re-dosed ammonium chloride back to 3 ppm

Most surprisingly though, I saw nitrate drop from 10 ppm down to 5 ppm on Day 8. I did the test twice, with additional shaking of the test solution, to rule out operator error and got the same results twice. The tests are brand new and don't expire until 2027. I have no plants and I've done no water changes.

Ammonia and nitrite seem to be getting consumed which indicates to me that the nitrosomonas and nitrobacter are becoming established.

I'll continue to monitor, but I'm trying to understand what might be causing a nitrate drop and whether I should be concerned?



My going hypothesis is that it’s due to my interpretation of the test result. The 5 and 10 ppm are just different shades of orange, so I suspect that maybe it’s just more or less flat at this point and not decreasing.

 

Just continue with the process...
In 4-5days it should be okay

 

I wouldn't be concerned about the nitrates. The nitrate test will not be accurate as long as you have nitrites present. There is no need to test nitrates it until you are getting zero ammonia and nitrites after 24 hours from dosing.

 

I wouldn't be concerned about the nitrates. The nitrate test will not be accurate as long as you have nitrites present. There is no need to test nitrates it until you are getting zero ammonia and nitrites after 24 hours from dosing.

This.

the nitrate test kit works by converting a portion to nitrite then measuring that as a proxy. So when nitrite is already present, nitrate measurements may not be accurate.

 

It's the matrix... why else would you be using it? Really the only reason I can see for a nitrate drop. The matrix is doing something. Nitrites become nitrates, it's an equal conversion at that step.

 

I'm a little over a month into my 75-gallon tank's fishless cycle and finally saw my first nitrite reading of zero (along with a corresponding spike in nitrate), so it feels like I'm getting closer to the finish line! While it's been tough to be patient I'm definitely getting a better handle on the interplay of the various variables at play in my water conditions.

About 11 days into the cycle I noticed a steep pH crash down to 6.0. After a 50% water change I got the pH back up to 7.4, followed by a subsequent dip to 6.6 two days later, a 35% water change, another pH drop, and a 50% water change. At this point I had dosed a total of 3.375 tsp of Fritz Pro Aquatics Ammonium Chloride. During this time I also started measuring my KH, which started at 5 dKH from the tap but dropped down to 2 dKH when the pH crashed.

At this point I did some reading and came across the baking soda method of increasing KH to help hold the pH steady while the bacteria colonies are building up. After that last water change I dosed 4 tsp of baking soda to bump up my KH to 6.

From that point forward I've seen a pretty steady and predictable cycle progress: Day 0 below is when I added the initial 4 tsp of baking soda and dosed ammonia to 4 ppm. Day 17 I finally got nitrite to zero and started measuring nitrate.




I've also seen the strong correlation between cumulative ammonia addition and the reduction in KH and pH. I did do another 80% water change and replenishment with 5 tsp baking soda on Day 10 after the KH dropped to 1 and pH dropped to 6.4







A pH crash at this point is all fine and good, aside from slowing down the cycling progress, but it got me to thinking about how to mitigate these crashes after I actually add fish. Presumably weekly 20-25% water changes will replenish some KH, but should I consider any additional buffers if my KH out of the tap is at 5 dKH? I understand that baking soda itself is not recommended when you have fish in the tank, and I don't particularly want to raise my pH at the outset since it's already slightly basic (7.2-7.4) out of the tap.

 

5 dkh is acceptable KH. you can get the KH drop due to nitric/nitrous acid, and carbonic acid from cycling due to all of the ammonia at once and your buffer KH banging up against it. the pH drops from free Hydrogen ions in the water.

As I understand your chart, you started with 4ppm ammonia, added 6 more ppm ammonia by day 5, 4 more ppm between day 5 and 10, and 4 more between day 10 and 17. I mean that's 18ppm ammonia if that is correct in about a half a month, averaging a little over 1ppm daily.

The fish are going to trickle ammonia and there would be a regular water change or two in that time period. Most folks aren't chemists or biologists, and just say "should process 2-4ppm ammonia all the way to nitrates in 24 hours or less".

Well, I'm here to say that will work, but it's pretty overkill. nobody can tell you how much ammonia a fish produces in 24 hours, reliably, it's variable and depends on lots of factors, but it's not a TON. and most folks can't tell you if that ammonia is toxic or not and how much of it is in toxic form, although some can, but it's a guessing game on what the fish actually produce based on temp, feedings, metabolism, ect. ect. on how much ammonia a fish produces, and then it's temp and pH on how much of that ammonia is toxic, and how much of it is ammonium and non-toxic.

Highly unlikely the tank and your fish are going to replicate this ammonia production and produce 6ppm ammonia per week much less in 2ppm spurts all at once. Also unlikely you will chip out the buffer like you are now once it's cycled, and highly unlikely the pH is going to drop out once plants or algae come into the picture and use up carbonic acids/ CO2, and then your buffer (KH) should stabilize the pH and release Hydrogen Ions when it needs acid, and hold them when it doesn't. maintaining the pH as long as you dont' get too neglectful with water changes. figure it like this, the acids of cycling as heavy as you are, eat away the KH buffer. you did the right thing by countering with adding more carbonates whether carbonate or bicarbonate, it's a counter buffer, same way pH down and pH up works. HOWEVER you have to be careful about doing that with fish in the picture, they can't handle wild swings of pH.


Even if you do let it ride, the pH can drop to 6. what it can't do is drop to 6 rapidly which is bad for the fish. you might have to limit the type of fish you keep if the pH thing is going to be a constant issue. you shouldn't have to amend to make it work after cycling, water changing should be more than sufficient.

dKH of 2 or lower is kind of sketchy,. 5dKH is fine.


You could draw a bucket of water from the tap, and test it, test it again after 15 minutes, then after 24 hours, than at 48 hours for something to do, see exactly how it's going to act as it gains the atmosphere and balances out, how it should act in the tank. if the pH rises or falls, ect. it's good to know what you are working with.

Also good to know when you add fish, how many nitrates you build over X amount of time between water changes and get a baseline. this will change also, but just good to know about how much builds up over the time between water changes, and how much of a water change you need to do to avoid a build up of nitrates,,,, or acids to keep it stable.

IF, the source water is treating the water, deionizing it, in order to raise the alkalinity, (removing acids like CO2) then as it sits, it will take on CO2 from the air, and produce acids which might lower KH and/or pH over time. checking how the tap water behaves after it leaves the pipes, might indicate what you'd need to do, or not do.

 

Highly unlikely the tank and your fish are going to replicate this ammonia production and produce 6ppm ammonia per week much less in 2ppm spurts all at once.

Thanks! This was my fundamental question. I figured the high levels of ammonia added at once during cycling are what's quickly eating up the carbonate buffer, and that this is not representative of what will happen with the ammonia from the fish in the tank.

You could draw a bucket of water from the tap, and test it, test it again after 15 minutes, then after 24 hours, than at 48 hours for something to do, see exactly how it's going to act as it gains the atmosphere and balances out, how it should act in the tank. if the pH rises or falls, ect. it's good to know what you are working with.

I should clarify that right out of the tap, the pH was actually around 8.4. When I initially filled the tank I just ran the filter and heater for a period of time before adding any ammonia to see where the pH would stabilize. It dropped from 8.4 to 7.2 within two days while circulating in the tank and held at 7.0 - 7.2 until its initial crash during the early stage of the nitrogen cycling process.

 

Over the last week my cycle has been progressing to the point where I've been fully converting 2 ppm of ammonia through to nitrates in 24 hours for several consecutive days (meaning ammonia and nitrite were both reading 0 ppm at 24 hours).

I decided to move to the next step, which was adding my live plants, but after doing so I observed that the nitrite conversion has slowed down considerably. Here are the things that I did before noticing this change:

• Prior to adding plants I did an 80% water change, using Seachem Prime for dechlorination, for a few reasons:
  • to remove nitrates that built up during the fishless cycle
  • to recharge my KH and boost the pH which was again on the verge of crashing
  • I found it easier to put the plants in with much of the water removed.
• Added my plants, which are a variety of low-light beginner plants (Anubias, java fern, dwarf sagittaria, vallisneria, cryptocoryne wendtii, and bacopa caroliniana)
• Added some root tabs and Easy Green Fertilizer from Aquarium Co-op.
• I did NOT add any baking soda to increase KH as I did during the fishless cycle
• I did drop the temperature - I was running at 82F before adding plants but now have reduced it to 78.5F to get it more in the range of what the fish will need.

I dosed ammonia to 1 ppm, just to keep the bacteria fed, as I'm hoping to start adding fish in the next week. The ammonia dropped to 0 ppm in 24 hours, but I still had 0.25 ppm nitrite after 24 hours. It did drop to 0 ppm at 27 hours. (Whereas I was previously seeing both ammonia and nitrite drop to 0 ppm after 24 hours with 2 ppm ammonia dosing).

I'm curious as to whether any of the above changes - particularly temperature, fertilizers or plants - may be contributing to a slow-down in nitrite conversion, and whether I should consider delaying the addition of fish at this point. Any input appreciated!

BTW, here's what my set-up looks like with plants

 

You have only been at the cycling process for 8 days. You are just getting started. I takes 6-8 WEEKS, not days for a tank to fully cycle.

Seachem Matrix is made from natural pumice volcanic rock. It has lots of deep pores within the structure. It is a good material for biomedia, much better than ceramic rings. Over time, some people say that the pumice can develop colonies of denitrifying bacteria that can convert nitrates to nitrogen gas, but those bacteria usuallly take months to establish themselves. They need anaerobic conditions deep within the pores. Nitrifying bacteria need oxygen to convert ammonia to nitrite and then to nitrate.

Since your tank has live plants, it is likely that those plants are consuming nitrates and ammonia to fuel their growth.

Bring the ammonia level to 2 ppm and then check it the next day. If the level drops to zero, you are well on your way to success. However, do not quit adding ammonia. Add 2 ppm each day until you see your nitrite levels peak and then stabilize at zero after 24 hours. You should see nitrates start to increase. If they get over 20 ppm, it is time to start doing water changes on a routine basis. At that time, you can safely add fish and quit adding ammonia. The fish food will be consumed and converted to fish waste which will continue the nitrogen cycle,

 

Thanks. To clarify, though, I have been cycling for about five weeks now, not 8 days. I've been regularly dosing ammonia to 2 ppm and having it drop to zero within 24 hours for several weeks, while nitrite levels continued to stay high. It was only about a week ago that nitrite started coming down, and since then it was regularly getting converted to nitrate within 24 hours, and I started seeing nitrates build up to 80-160 ppm.

My question is about why the nitrite conversion seems to have slowed down again after the temperature change and plant/fertilizer additions.

 

Rayclem, Day 8 was like a month ago already. This person has been cycling for over a month.

Alkuhs , I'm not sure if the roughly 4 degrees is enough to slow the nitrification that much, but plants are bioload, and there is ammonification due to dead biological material that happens with living things. and temperature does slow nitrifier replication somewhat as well as pH slowing it.

Root tabs generally have some form of nitrogen in them, ammonia, or urea or nitrates, this release and addition could be a bit much for your nitrite breaking colony to quite handle above what you'd normally be doing ( since the nitrate breakers come last. the colony will continue to size up though. Stay the course a little longer before adding fish, each day the colony is doubling in size. Your nitrate breakers aren't quite there yet. your addition of plant and root tabs and temp change and small delay of nitrite turn over is showing you that. it's a positive you didn't get ammonia reading and just say nitrites take a couple house longer to turn over completely. Almost there, just a bit longer.

 

Rayclem, Day 8 was like a month ago already. This person has been cycling for over a month.

Alkuhs , I'm not sure if the roughly 4 degrees is enough to slow the nitrification that much, but plants are bioload, and there is ammonification due to dead biological material that happens with living things. and temperature does slow nitrifier replication somewhat as well as pH slowing it.

Root tabs generally have some form of nitrogen in them, ammonia, or urea or nitrates, this release and addition could be a bit much for your nitrite breaking colony to quite handle above what you'd normally be doing ( since the nitrate breakers come last. the colony will continue to size up though. Stay the course a little longer before adding fish, each day the colony is doubling in size. Your nitrate breakers aren't quite there yet. your addition of plant and root tabs and temp change and small delay of nitrite turn over is showing you that. it's a positive you didn't get ammonia reading and just say nitrites take a couple house longer to turn over completely. Almost there, just a bit longer.

I was looking at the graphs and failed to notice that the original post was in early July.

Hopefully, things are moving rapidly to completion.