Question: Tank Chemistry Q's

Okay, so I've went a bought a "Master Test Kit", and have been testing here and there to figure out how to get my tanks the best they can be.

On my relatively new tank (going on the 3rd week). I've been doing weekly water changes. I tested 2 days ago, before water change my levels were:

pH: 6.6
Ammonia: 0.25ppm
Nitrites: 5.0ppm
Nitrates: 20ppm
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AFTER the water change looks like this:
pH: 7.0
Ammonia: 0ppm
Nitrites: 0ppm
Nitrates: 10ppm

Question #1: Whats up with the pH change? It's also different in my Adult Axolotls cage (6.6/6.8)

Question #2: The first was displaying part of cycling correct? With the nitrites/nitrates high, and ammonia pretty low?

Question #3: I did a water change (I took about 2g out, that was the bucket size) from a 20L, which wasn't totally full to begin with, I probably took out 1/3 of the water that was in there. Replaced with fresh dechlorinated water, to 1" from the top.

Why was my nitrate drop so small? From 20ppm to 10ppm. It should have dropped alot more IMO because I removed water, and diluted the water that remained!

First question; is this tank cycling empty, or are there animals in it?

I'm not sure about the PH change: is there anything in the tank, any decorations or something that could have caused it?

Since you have nitrates your tank is almost cycled, yes. Nitrates are the final product of the cycle and the least toxic of the three so 10 ppm is perfectly acceptable in a freshwater tank. Ammonia and nitrite are the ones that should be kept at 0.

Yes the tank has an axolotl in it. I got the tank as soon as I got the axolotls. Not the perfect set up I know.

I have river rock in the tank. Could that be it? I had some artificial resin stuff but it smelled the tank up horribly with chemical smell.

You need to be doing water changes more often if there is an axolotl in the tank. 5ppm nitrite is extremely high and could potentially be harmful to it's health.

I don't think the river rock could have changed it....? unless it's a porous rock. Are you 100% sure you're reading the tests correctly?

Also out of curiosity, how big are the rocks? Anything even remotely smaller than the Axolotl's head poses an impaction risk, just have to check.

Sounds like your tank is on it's way to cycling, but isn't there yet.

Have you tested your tap water? It could be that the extra nitrates and pH changes are due to your tap water.

As long as you have evidence of a cycle starting and you change the water whenever the ammonia or nitrites get too high it will all come together eventually.

The rocks are bigger than my hands. I have no substrate. I've been doing weekly water changes, is this not enough?

Swampie said:

The rocks are bigger than my hands. I have no substrate. I've been doing weekly water changes, is this not enough?

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You need to change the water more often during a fish in cycle. Letting the levels get above 1ppm can be dangerous to the animal's health. Test daily and do changes as needed.

When I was re-cycling my tank I had to do multiple changes daily to keep the levels out of the danger zone.

Kaini said:

You need to change the water more often during a fish in cycle. Letting the levels get above 1ppm can be dangerous to the animal's health. Test daily and do changes as needed.

When I was re-cycling my tank I had to do multiple changes daily to keep the levels out of the danger zone.

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If you have one axolotl it might even be easier to remove it and place it in a smaller container that way you can do 100% water changes for your axolotl, then do a fishless cycles on you tank. The tank would be able to cycle much quicker.

Aquarium chemistry is hydrochemistry on a small, confined scale. That adds some complexity to it, but nothing that can't be figured out.

This link: The Nitrogen Cycle - Article at The Age of Aquariums - Tropical Fish provides a pretty solid overview of the chemistry of the nitrogen cycle in an aquarium. Though it mentions that nitrate (NO3) can be removed via water changes or the additon of live plants, it doesn't explain that a deep substrate can also help remove nitrate through the activity of anaerobic bacteria (which, in short, make diatomic nitrogen [N2] that off-gasses back into the atmosphere). Note that I'm not advocating a deep substrate for your animals, just adding a bit of information for the sake of completeness. The optimal types and quantity of plants for nitrate removal aren't discussed, either.

I'll have a go at your questions:

Q1: The pH change is likely due to your removing the majority of the nirtogenous wastes compounds from the water. In higher concentrations, the nitrogenous compounds present in an aquarium (NH3/NH4+, NO2, and NO3) can lower the pH of water, as can excess concentration of CO2 (via carbonic acid). If you're using "river rocks" in your tank, they're most likely comprised of granite or bassalt, both of which will have a negligable effect on your pH.

Q2: Yes, your tank appears to be "cycling" (establishing the microorganisms responsible for moving nitrogenous waste through the nitrogen cycle). It doesn't appear to have completed the cycle, though, and still needs a little time.

Q3: How long after you did the water change was your water tested? I'm honestly surprised that you saw a 50% decrease in the nitrate concentration with you only removing ~30% of the water. The nitrate should have been evenly distributed throughout the system (water column). Using a concentration/dilution ratio, you should have only seen ~30% reduction in nitrate if measured "immediately" after the water change. You essentially diluted by 1/3. I would expect to see ~15 ppm nitrate after a water change of that size and based on your initial concentration. Think about it like this: You had 20 ppm NO3 in your tank water. You remove 2 gallons. Both the water you removed AND the water remaining in the tank still have 20 ppm NO3. You add 2 new gallons of water (hypothetically nitrate free, though it might not be... but I won't get into that here), diluting the nitrate-rich water in your tank with 2 gallons.

However, the elimination of ammonia and nitrite indicates that you waited some time (a half hour, maybe?) after the water change to take the readings. If the ammonia source was removed during the water change, what little was left in the water was likely converted to nitrite, then to nitrate. If no more source of ammonia was introduced (waste, decomposing food, etc.) between the water change and the testing, all of the ammonia and nitrite would have been converted into nitrate (fairly quickly), so nitrate be the only nitrogenous compound seen... and it was. It all makes sense.

Here's another interesting link regarding the aquatic nitrogen cycle: http://www.na.fs.fed.us/spfo/pubs/n_resource/wetlands/wetlands7_biogeochemical cycles.htm, if you care to dive further into this.

Hope this helps,
-Cole

Kaini said:

You need to change the water more often during a fish in cycle. Letting the levels get above 1ppm can be dangerous to the animal's health. Test daily and do changes as needed.

When I was re-cycling my tank I had to do multiple changes daily to keep the levels out of the danger zone.

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Please excuse my ignorance, which level are you talking about? Any of them?

Swampie said:

Please excuse my ignorance, which level are you talking about? Any of them?

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Ammonia and Nitrite. Anything over 1ppm is toxic. As I said before, Nitrate is the final product of the cycle and is less toxic - anything under 40 ppm is considered acceptable in a freshwater tank.

Since you have nitrates your tank is almost cycled, yes. Nitrates are the final product of the cycle and the least toxic of the three so 10 ppm is perfectly acceptable in a freshwater tank. Ammonia and nitrite are the ones that should be kept at 0.

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Sorry to have to repeat myself If I can do anything to be more clear, tell me!

Edit: Also you should totally read Cole Grover's post if you haven't! while a little in depth and daunting it's good information!

Sorry, I missed that part of the comment. Thank you for your help. I'm doing another water change now, and am going to test before and after the change to see what will happen. Just really curious! Also, will be removing the axolotls and put them in a temporary tank until the tank finishes cycling.

I think this will be a good time to add my sand to the bottom of the tank, since they wont be in there. Is this okay?

As good a time as any to add the sand I suppose. Remember if you remove the axolotls you'll need to provide another source of ammonia for the bacteria to feed on.