Why did my levels change overnight?

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Water_Bubbles

Aquarium Advice Newbie
Joined
Jun 21, 2024
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Location
arizona
I’m a bit new to fish keeping, but I do understand some of it. I have an API master test kit that I’ve been using to keep track of my levels.

For the last week I’ve been dealing with high nitrates with 0 nitrites and 0 ammonia. I’ve been doing water changes and checking my nitrates every day and they still haven’t done gone down. Yesterday I performed a 60% water change which I finally noticed that my nitrates were down to about 10-20. (They were about 40-80 before). I was relived that I finally got them down somewhat.

I went to bed and when I woke up this morning, my tank was super cloudy and so I checked my levels and sure enough my nitrates shot back up again and now I have some ammonia in my tank. How did this happen overnight? And how can I keep my nitrates down?


Questions you might ask:
The only thing I changed yesterday to my tank was the 60% water change. (I use prime as my conditioner) and I put 5ml of plant food into the tank for my plant

I have a 10 gal tank with 1 balloon Molly and one panda Molly and 15 of my other balloon Mollys babies in a net. (Momma unfortunately passed away last week)

I did go out and buy a plant for my tank as I read it’ll help reduce nitrates but I haven’t seen a change yet

I have done a 60% water change in the past but I’ve never gotten ammonia afterwards or it making my tank so cloudy

I feed the babies 3 times a day (morning, afternoon and night. They are about 3 weeks old). I feed the adult mollys every other day

I used to do weekly water changes but because my nitrates were so high I started doing them every day. I started with doing 25% then 30% the next day then 40% the next day etc till 60% yesterday

I did check the nitrates of my tap water and that is photo #3. The first photo is my levels yesterday and the second photo is my levels today

Any advice will be greatly appreciated
 

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Do you know if your tap water is treated with chlorine or chloramine? Chloramine is chemically bonded chlorine and ammonia, so if your water is treated with chloramine every water change will add a little ammonia until your cycle converts it to nitrate. A test of your tap water for ammonia will test positive if your water is chloramine treated.

Nitrate rising is normal in between water changes. The nitrogen cycle consumes ammonia and puts out nitrate. Your nitrate is then reduced through a water change. Your tap water has some nitrate in it, so a water change won't have as much of an effect as it would if your tap water was zero nitrate.

If you are seeing ammonia and higher than normal nitrate this is due to higher than normal ammonia going into the tank. Its possible this is from the molly fry getting bigger and the food increasing accordingly. The nitrogen cycle grows and dies off in relation to the amount of food (ammonia). If more ammonia is introduced then it takes a while for the nitrogen cycle to catch up with a higher amount. And once its cycled out you will see more nitrate.

While adding plants do use nitrogen in form of ammonia and nitrate, most commonly kept aquarium plants arent going take up enough to be noticable in your testing. If you went quite heavy in your planting, and/ or used high nutrient demand you may see some effect over time.

To give you some comfort the amount of ammonia in your test is practically zero. Its not going to cause any issues, especially in such acidic water. Ammonia gets more toxic with higher pH. I would consider the ammonia in your test to be zero.

Im not really any kind of expert on breeding, but 2 mollys and 15 fry in a 10g tank seems a lot. You should probably be doing big daily water changes.

Do you know your general hardness and carbonate hardness? If you dont have a test could your water company tell you? Could you get a local fish store to test for you?
 
Thank you so much for your advice. I have to leave for work soon so all I could get for you at the moment was the ammonia of my tap water. I’ll respond back with everything else after my shift is over
 

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There is a slight greenish tinge to your tap water test. It could indicate chloramine or could just be a slight inaccuracy in the testing which isnt uncommon. They are home test kits, not laboratory testing. Id ask your water company how they treat your water, but even if it is chloramine its very low level. Not enough to account for any levels being higher than normal.
 
Do a pH test with the regular test ( not the high range pH reagents) to get a more accurate reading on your level. As Aiken stated, Ammonia becomes less toxic ammonium when the pH is below 6.8. Low Range pH tests would have a blue, yellow or green reading, not brown. Once you know your correct pH level, you'll know whether to panic :oops: or not about any ammonia on your tests.

There are a few options to remove nitrates besides water changes. Plants ( not all but certain ones are real nitrate absorbers ) nitrate removing pads ( I've really loved Polyfilters: POLY-BIO-MARINE, Inc. in my freshwater and saltwater tanks) are the easiest 2.

Lastly, how old is the tank and did you go through the " cycling" period when you set up the tank? ( I expect the answer is yes but I have to ask. ;) )
 
Do a pH test with the regular test ( not the high range pH reagents) to get a more accurate reading on your level. As Aiken stated, Ammonia becomes less toxic ammonium when the pH is below 6.8. Low Range pH tests would have a blue, yellow or green reading, not brown. Once you know your correct pH level, you'll know whether to panic :oops: or not about any ammonia on your tests.

There are a few options to remove nitrates besides water changes. Plants ( not all but certain ones are real nitrate absorbers ) nitrate removing pads ( I've really loved Polyfilters: POLY-BIO-MARINE, Inc. in my freshwater and saltwater tanks) are the easiest 2.

Lastly, how old is the tank and did you go through the " cycling" period when you set up the tank? ( I expect the answer is yes but I have to ask. ;) )
Here is the PH of my tank. I’m shocked because my PH is almost always 7.4.

As for the nitrate pads, I dont have that exact brand but I did go out and buy nitrate pads the same day that I got my plant. I have it in my filter right now and I don’t know if it’s a slow change but I haven’t seen a difference yet

My tank is about 5 months old. I really wish I could say it was cycled first but it wasn’t. It was my litter sisters tank that I realized wasn’t getting adequately taken care of so I took it home and now I’m working on getting it cycled. I’ve lost a lot of fish in the process.( I started with had 4 mollies, 2 Cory’s catfish, 2 African dwarf frogs, and 2 snails)

My levels were completely fine till about a week ago which thanks to @Aiken Drum I realize it’s probably due to the Molly fry

I’m glad my Nitrites are at 0 but I’m still curious as to why my ph, nitrates and ammonia all suddenly raised by a water change that I do all of the time. And the fact that my water looks milky now instead of being clear like it used to be. I also noticed I have brown algae growing everywhere

For my tank, do you guys suggest just keeping up with water changes? I honestly don’t what else to do
 

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Do you know if your tap water is treated with chlorine or chloramine? Chloramine is chemically bonded chlorine and ammonia, so if your water is treated with chloramine every water change will add a little ammonia until your cycle converts it to nitrate. A test of your tap water for ammonia will test positive if your water is chloramine treated.

Nitrate rising is normal in between water changes. The nitrogen cycle consumes ammonia and puts out nitrate. Your nitrate is then reduced through a water change. Your tap water has some nitrate in it, so a water change won't have as much of an effect as it would if your tap water was zero nitrate.

If you are seeing ammonia and higher than normal nitrate this is due to higher than normal ammonia going into the tank. Its possible this is from the molly fry getting bigger and the food increasing accordingly. The nitrogen cycle grows and dies off in relation to the amount of food (ammonia). If more ammonia is introduced then it takes a while for the nitrogen cycle to catch up with a higher amount. And once its cycled out you will see more nitrate.

While adding plants do use nitrogen in form of ammonia and nitrate, most commonly kept aquarium plants arent going take up enough to be noticable in your testing. If you went quite heavy in your planting, and/ or used high nutrient demand you may see some effect over time.

To give you some comfort the amount of ammonia in your test is practically zero. Its not going to cause any issues, especially in such acidic water. Ammonia gets more toxic with higher pH. I would consider the ammonia in your test to be zero.

Im not really any kind of expert on breeding, but 2 mollys and 15 fry in a 10g tank seems a lot. You should probably be doing big daily water changes.

Do you know your general hardness and carbonate hardness? If you dont have a test could your water company tell you? Could you get a local fish store to test for you?
My hardness says it’s about 300 but I used a test strip from Walmart so I know it’s not going to be super accurate. I would have to get my fish store to test for me when I get the chance

I originally got my balloon Molly from Petco and I wasn’t expecting her to be pregnant so when a bunch of babies showed up, I definitely was unprepared. I was able to separate them in time before my panda Molly ate all of them and get them into a breeder net which is what they are in now
 
Here is the PH of my tank. I’m shocked because my PH is almost always 7.4.

As for the nitrate pads, I dont have that exact brand but I did go out and buy nitrate pads the same day that I got my plant. I have it in my filter right now and I don’t know if it’s a slow change but I haven’t seen a difference yet

My tank is about 5 months old. I really wish I could say it was cycled first but it wasn’t. It was my litter sisters tank that I realized wasn’t getting adequately taken care of so I took it home and now I’m working on getting it cycled. I’ve lost a lot of fish in the process.( I started with had 4 mollies, 2 Cory’s catfish, 2 African dwarf frogs, and 2 snails)

My levels were completely fine till about a week ago which thanks to @Aiken Drum I realize it’s probably due to the Molly fry

I’m glad my Nitrites are at 0 but I’m still curious as to why my ph, nitrates and ammonia all suddenly raised by a water change that I do all of the time. And the fact that my water looks milky now instead of being clear like it used to be. I also noticed I have brown algae growing everywhere

For my tank, do you guys suggest just keeping up with water changes? I honestly don’t what else to do
PH changes can occur due to a change in aeration, acidic conditions in the water and calcium based decorations to name a few. In your case, with the pH falling, it's most likely from the acidic conditions from the ammonia. I suggest you take a sample of your source water and leave it overnight THEN test the pH to see what it's actual level is. If you test the pH too soon after a water change, you will get a false reading until the water settles.

The brand of the nitrate pads will matter so you know whether to replace them with a different brand or the same one if it's working. Just an FYI, you want your water to go through this kind of pad last before returning to the tank because you do not want it to remove anything else your biological filter bed needs to grow before they get to it. You only want it to remove the end product, nitrates.

At 5 months, you may have just actually finished cycling your tank. The milky water is typical of a bacteria bloom in uncycled and newly cycled tanks that do not have a mature biological filter yet. That you had a rise in ammonia says yo me that you disturbed too much of this biological filter bed so it had not grown enough to compensate for the loss from the water change. Did you change the filter pads in the filter and/or disturb the substrate when you did the large water change?

Brown algae ( actually a diatom) is another sign of an immature tank and feeds off the higher nitrogen level. Other than it's unsightly appearance, it should not harm your fish and will go away once you get your nitrate level under control. FYI: Using one plant to combat Nitrates will not be very effective unless it's a plant that really sucks up nitrates such as Hornwort, Anacharis and some of the floating plants like Duckweed or frogbit. ( Beware tho that these floating plants will quickly overpopulate in a tank with high nitrates. )

Bottom lining all this: your big mistake was changing too much water too soon. You probably either disturbed the bacteria bed ( a.k.a Biological filter) or you removed some of it. The milky water was the result of this. I suggest not changing any more water until your water clears up naturally. You can still use the nitrate absorbing pads as long as they are placed so that the water going into the tank goes through the pad last before the tank. You can also help reduce the nitrates by using bottled water that contains no chloramines or nitrates so that when you change water, you are actually diluting the nitrate level.
A 10 gallon tank unfortunately is not a good tank for Mollies as they can overpopulate it rather quickly ( as you found out). With such a small water volume, it can go haywire rather quickly. Once the tank has settled, you can get into a water change schedule based on the amount of nitrate in the water. We have another member here who also had a nitrate issue in her 6.5 gallon tanks because her tap water was high in chloramine so every time she changed her water to reduce her nitrate level, she was actually adding a lot of ammonia thanks to using PRIME which her biological filter was converting into nitrates so she wasn't really gaining any ground until she switched to bottled spring water so that the only source for nitrates was the fish themselves. That may end up being your solution as well unless you go with the plants recommended as high nitrate absorbers.

Hope this helps. (y)
 
PH changes can occur due to a change in aeration, acidic conditions in the water and calcium based decorations to name a few. In your case, with the pH falling, it's most likely from the acidic conditions from the ammonia. I suggest you take a sample of your source water and leave it overnight THEN test the pH to see what it's actual level is. If you test the pH too soon after a water change, you will get a false reading until the water settles.

The brand of the nitrate pads will matter so you know whether to replace them with a different brand or the same one if it's working. Just an FYI, you want your water to go through this kind of pad last before returning to the tank because you do not want it to remove anything else your biological filter bed needs to grow before they get to it. You only want it to remove the end product, nitrates.

At 5 months, you may have just actually finished cycling your tank. The milky water is typical of a bacteria bloom in uncycled and newly cycled tanks that do not have a mature biological filter yet. That you had a rise in ammonia says yo me that you disturbed too much of this biological filter bed so it had not grown enough to compensate for the loss from the water change. Did you change the filter pads in the filter and/or disturb the substrate when you did the large water change?

Brown algae ( actually a diatom) is another sign of an immature tank and feeds off the higher nitrogen level. Other than it's unsightly appearance, it should not harm your fish and will go away once you get your nitrate level under control. FYI: Using one plant to combat Nitrates will not be very effective unless it's a plant that really sucks up nitrates such as Hornwort, Anacharis and some of the floating plants like Duckweed or frogbit. ( Beware tho that these floating plants will quickly overpopulate in a tank with high nitrates. )

Bottom lining all this: your big mistake was changing too much water too soon. You probably either disturbed the bacteria bed ( a.k.a Biological filter) or you removed some of it. The milky water was the result of this. I suggest not changing any more water until your water clears up naturally. You can still use the nitrate absorbing pads as long as they are placed so that the water going into the tank goes through the pad last before the tank. You can also help reduce the nitrates by using bottled water that contains no chloramines or nitrates so that when you change water, you are actually diluting the nitrate level.
A 10 gallon tank unfortunately is not a good tank for Mollies as they can overpopulate it rather quickly ( as you found out). With such a small water volume, it can go haywire rather quickly. Once the tank has settled, you can get into a water change schedule based on the amount of nitrate in the water. We have another member here who also had a nitrate issue in her 6.5 gallon tanks because her tap water was high in chloramine so every time she changed her water to reduce her nitrate level, she was actually adding a lot of ammonia thanks to using PRIME which her biological filter was converting into nitrates so she wasn't really gaining any ground until she switched to bottled spring water so that the only source for nitrates was the fish themselves. That may end up being your solution as well unless you go with the plants recommended as high nitrate absorbers.

Hope this helps. (y)

Thank you so much for your advice!! I left my water alone for about 3-4 days as the cloudiness slowly started to go away then I did a 25% water change 2 days ago with Crystal Geyser spring water (as you suggested) and now my water is clearer than ever

I waited until today to check my levels (since you said that the PH won’t be accurate if you check it after the water change) and my levels are attached to the photo below

Edit: Also fyi my nitrate pad is the one that’s last before the water gets into the tank
 

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Okay, so based on the colors I see, your pH is slightly alkaline ( 7.2 ish) which means that any ammonia in the tank ( whether from the fish or from chloramines) will not be ammonium so toxic to the fish the higher it goes. Your nitrates look lower than in the first pics of this thread. It's going to take more than one 25% water change with non chloramined water for it to make a major difference. I would say your nitrate pad is not working if it's been in there for more than a week. I would change it out and compare the nitrate reading before your next water change. If you see no change or it continues to rise, it's time to change brands of pads. IMO

As for the clearness of the water, Spring Water does do wonders. ;) (y)
 
Again thank you for responding to me and helping me out!!

I will take my nitrate pad out now lol

To keep my nitrates down, how much should I change the water and how regularly? Should I do 50/50 tap water and spring water or just 100% spring water per water change?
 
Again thank you for responding to me and helping me out!!

I will take my nitrate pad out now lol

To keep my nitrates down, how much should I change the water and how regularly? Should I do 50/50 tap water and spring water or just 100% spring water per water change?
Until you get the nitrates under control, I would continue with the 100% spring water and I would change water 2 times per week. Once you get the numbers to reasonable levels, you can try a 50/50 mix and see how much the nitrates rise in a 48 hour period then decide from there. If it rises a lot, I would stay with the spring water or get plants that are high nitrate absorbers if you don't want to use Nitrate removing pads. ( Speaking of which, I said to replace the pad not just remove the one you had in the filter to see if they really are removing nitrates. ) Once you get things under control, you can cut back to doing water changes once a week. (y)
 
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