# Adding Oxygen to an NPT?



## Moose-Factory (Feb 13, 2008)

I have an 85 gallon heavily planted NPT that I would like to add more fish to. However, every time I attempt to introduce new fish, either the newly introduced fish or some of my old ones will die the very next day.

Either the new fish will be dead in the tank, or if it's the old fish that die, usually I'll find them on the floor outside the tank (rimless). This always happens after the very first evening after adding new fish.

During the day, the fish exhibit entirely normal behaviors and all water parameters are normal. So what is going on?

My only theory is that the fish combined with the plants respiration are using up all available O2 at night, and they are dying that way?

I would try adding an airstone on a timer to go on at night, but I had heard using airstones in NPT's was a no-no, but forgot why.

Anyway, is my hypothesis possible for my problem, and could I use an airstone at night without ill-effect to the plants?


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## Michael (Jul 20, 2010)

How many fish of what size do you have in this tank?

Yes, your hypothesis is possible, and if so it means that the tank is right on the border of being overstocked with fish. If you want more fish, you may need to get another tank.

Airstones are not used in Walstad tanks because they cause the loss of too much natural CO2. But Walstad tanks are normally not overstocked. An airstone might enable you to add a few fish, but if overstocking is the problem you will be flirting with more fish deaths.

Bacterial respiration also uses oxygen and produces CO2. Is there a lot of decaying matter in the tank or filter(s)?


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## Moose-Factory (Feb 13, 2008)

Thanks Michael, good points. There are about 30 fish in the tank (14 neon tetra, 6 dwarf neon rainbowfish, 6 harleq rasbora, 2 SAE, 1 pearl gourami- plus innumerable pond snails, MTS, and cherry shrimp.

I hadn't though about the bacteria respirating too, which would exacerbate the O2 issue if that's what it is. It seems as though if I want more fish, solving this O2 issue would allow me to stock more (but if I have this correct, using a stone would deprive my plants of CO2?)

Basically, I would like more fish- if I'm at my tanks limit I'd like to find a way to up my capacity, hence the airstone idea.

Could I use the airstone at night when the O2 is needed, and then could I supplement lightly with CO2 during the day to make up for the CO2 loss from using the airstone at night? I know this would technically be stepping over the bounds of a traditional NPT, but I'd be ok with that if I could have more fish. The challenge I'd like to solve is how to do this without throwing everything that's so carefully balanced in an NPT out of whack.


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## John Barrett (Feb 14, 2017)

Just a thought but could an oxydator help? I was thinking maybe Michael could answer this if he has had any experience with or knows more about them. I have been reading up on them and it seems it would add 02 without depleting c02. No surface agitation involved as with an air stone.


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## Michael (Jul 20, 2010)

Seeing your fish list, I don't think the tank is overstocked at all. So we need to look for other problems. Maybe a very thorough vacuuming would reduce decaying material. Probe the substrate to see if it releases foul-smelling bubbles. This would indicate hydrogen sulfide, a symptom of anaerobic substrate.

I notice that you have canister filter(s) on the tank, but it may need more circulation. Try a powerhead instead of an airstone. This will increase circulation, but not cause as much loss of CO2 as an airstone.

If it makes you feel any better, during a multi-day power outage I had similar problems in two of my tanks. No light and no circulation allowed CO2 to build up and kill some sensitive fish. Big water changes and restored power stopped the deaths.


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## hoppycalif (Apr 7, 2005)

When you find fish on the floor you can be sure they got there by jumping out of the tank. Fish which are dying in the tank from anything, other than "combat" with other fish aren't likely to jump out of the tank. For example, when you have too much CO2 in the water, that can kill the fish, but even though they go to the water surface, usually at a corner of the tank, they don't jump out. They just die and float or sink.

My guess is that adding more fish leads to either the new fish attacking the old fish, or vice versa, and to get away from that the attacked fish, or the scared fish, jump out. I doubt that you have nearly enough fish in that size tank to be overstocked.

I don't know much about dwarf neon rainbow fish, so I'm going to blame them!!


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## Michael (Jul 20, 2010)

Hoppy has a good point. If aggression is the problem, my bet is on the pearl gourami. They sometimes become aggressive, especially if kept as single fish. In a group they tend to scrap among themselves and leave other fish alone.


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## hoppycalif (Apr 7, 2005)

Michael said:


> Hoppy has a good point. If aggression is the problem, my bet is on the pearl gourami. They sometimes become aggressive, especially if kept as single fish. In a group they tend to scrap among themselves and leave other fish alone.


Sure, blame it on the big guy


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## Moose-Factory (Feb 13, 2008)

hmm, a lot to think about. I'm currently using an eheim 2217 cannister filter, which has a flow rate of 264 gph. It will be a little less than that flowing through tubing and UV filter, but is this about sufficient?

No bubbles or gas pockets in the soil, I spread it relatively thin when setting up the tank (1" top soil, 0.75" capping stones). 

There very well could be excess decaying material in the tank. However, this is a problem I can't really solve as I can no longer vacuum my tank; My snails (MTS, nerites, or something!) have completely churned up the substrate, such that the former capping layer is now entirely intermixed with the topsoil substrate. Basically I now have a topsoil tank which I can't vacuum without sucking up the soil. 

As far as aggression, it's possible they get agressive when I'm not around, but when I'm there I've never seen any. The female pearl gourami really minds it's own business- as do all the fish, for that matter- no chasing or nipping- the zebra danios are the only ones that will sometimes chase each other. 

Could I have too many shrimp? They simply keep multiplying, I'm sure I have hundreds in the tank from the 17 I started with. Could they be filling up the capacity my tank is able to support?


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## Michael (Jul 20, 2010)

One Eheim 2217 for a tank as long and densely planted as yours probably isn't enough. The general rule on circulation is that the gph of all filters and powerheads shouild be equal to 5 to 10 times the total volume of the tank. So in your case this would be 400-800 gph. I think the high end of the range is helpful in densely planted tanks--the plants really slow down the circulation.

Try a powerhead at the diagonal corner opposite your filter output to create a circular flow pattern.

It is hard for me to believe the shrimp are the problem, but it's possible.


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## Moose-Factory (Feb 13, 2008)

Well, disaster has struck... I topped up my tank with about 4 gallons of treated water, and also cleaned by filter tubing (nothing I haven't done a million times before). But last night, about a half hour later, I lost about a third of my remaining fish :wacko:. Was not expecting this.

MY tetra school is pretty much dead after last night, as are most of my harlequin rasboras. The Gourami, SAE, and dwarf neon rainbowfish school survived and are looking ok. I'm at my wits end here.

I have a new powerhead on order as per your suggestions to increase flow, hopefully that helps but is something else going on?


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## Michael (Jul 20, 2010)

That is terrible! And I have no idea what is going on.

How long has it been since you did a large water change? Do you have any idea what your total dissolved solids (TDS) is? I'm grasping at straws.


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## John Barrett (Feb 14, 2017)

I notice the basics have not been asked. Where is your water coming from and what do you use to treat it? I made the mistake when starting of not using a conditioner that broke down chloramines. Fish lived but suffered. Are you dosing anything? How long has the tank been running and did you get it used? If your shrimp amd mts are still ok and fish are dying something really odd is going on. Also are you topping off with ro/di water? If you are topping off with treated tap water every time you need it, things could have been building up for a while and the last addition could have pushed it over the edge for some of the fish.


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## hoppycalif (Apr 7, 2005)

Four gallons of new water in an 85 gallon tank isn't likely to do any harm even if you did nothing to treat it. What did you do when you cleaned the tank, etc? What do you dose, especially what did you dose after you added the water, and in what quantities? Did you disturb the substrate? If I had to guess what is wrong I would start by guessing it is the substrate. What are you using as "topsoil"? And, what kind of gravel are you capping it with?


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## dwalstad (Apr 14, 2006)

Moose-Factory said:


> Well, disaster has struck... I topped up my tank with about 4 gallons of treated water, and also cleaned by filter tubing (nothing I haven't done a million times before). But last night, about a half hour later, I lost about a third of my remaining fish :wacko:. Was not expecting this.
> 
> MY tetra school is pretty much dead after last night, as are most of my harlequin rasboras. The Gourami, SAE, and dwarf neon rainbowfish school survived and are looking ok. I'm at my wits end here.
> 
> I have a new powerhead on order as per your suggestions to increase flow, hopefully that helps but is something else going on?


Dear Moose Factory,

I am so sorry to hear about your problem. This is truly a tragedy, one that would have caused me to run outdoors and start screaming.

It sounds like a _very_ potent toxin in your "treated water." If all you did was add 4 gal, and the fish started dying, then--as improbable as it sounds--it must be something in the water you added. It could be a neurotoxin. This would explain fish jumping out of the tank.

I would treat any water added to this tank with _fresh_ activated charcoal beforehand. I would keep fresh activated charcoal in our filter. Change it every two weeks.

There's also a very slim chance that it could be an electrical problem. Voltage running through the tank from overhead lights. Some circuit not grounded. This would cause fish to jump out of tank.


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## John Barrett (Feb 14, 2017)

The problem may be simple. Lets say I had a npt/walstad and I did not need to do water changes often. If it was soft water and every time it evaporated I added the same said soft water to fill it again, what would happen to the water in the tank over time? Wouldn't it turn to hard water with a dangerously high tds? Said water would test A/N/N just fine. If I had rasboras (which prefer low dissolved mineral content water) and red cherry shrimp (which could care less if acclimated over time) and the rasboras died after a long period of time, could it attributed to this? Would said water make it difficult for new fish to acclimate as well as more so stress already stressed soft water fish when adding new tank mates? I think this may be where Michael was headed when asking about the tds. I really am just trying to help and am sorry if stepping on anyone's toes here. I just spot that no one seems to have noticed he said he used treated water to top off the tank and did not say he did a four gallon water change. I sure don't treat my distilled water when topping off and this gave a clue.


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## Moose-Factory (Feb 13, 2008)

Ok, thanks everyone for the feedback.

I think I may have a clue of the problem now, maybe. I opened up my canister filter today in my general investigations into what may be going on, and it was way WAY dirtier and built up in there than normal- almost muddy.

Well, actually, it quite literally may have been a bit muddy in there because of the problem with my substrate I mentioned earlier- to reiterate, my nerites, MTS or something has folded over my substrate capping layer into the underlying topsoil- such that I basically now have an uncapped topsoil layer for my substrate now. 

Now here is part of what may have happened; as I mentioned the canister was filthy / mucky inside way beyond what it normally would be between cleanings- I then remembered I had removed my intake's pre-filter two or three weeks ago hoping to improve my flow rate.

With the pre-filter off, any time I've been adding water to the tank some of the soil substrate is kicked into the water column, and without the prefilter some of that soil must have been going directly into the canister filter to gum things up down there much faster than usual (leading to the mess in there I found today), whereas before most of that kicked up soil would never have made it into the canister and would have been caught and cleared when I regularly cleaned the prefilter sponge. 

Anyway, that's the only thing that definitely seems new and unwanted going on in the tank that I was able to find.

Other notes: the tank has been up for about 2 years. The original topsoil I dug from the woods behind my house. Water changes / additions are pre-treated with Prime. The only regular additions / supplements to the tank are fish food, potassium chloride (2 tsp once per month), and cuttlebone for the soft water I have.


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## John Barrett (Feb 14, 2017)

Moose-Factory said:


> Water changes / additions are pre-treated with Prime.


Is the water you add because of evaporation in your tank the same as the water you do changes with?


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## dwalstad (Apr 14, 2006)

I think you have discovered the problem. Good detective work!

Canister filters can be dangerous, because the media inside the canister is sealed. If gunk builds up too much, the whole system can go anaerobic and kill the bacteria inside. Then, the dead bacteria release their toxins into the water. 

This happened to me when the power went out for a few hours in my tank (mentioned in my book, page 73). When I turned on the canister filter, I could see a little debris coming out. Didn't think anything of it until the fish started dying a few hours later. What happened was the canister bacteria suffocated, died, and released their internal chemicals, which are just non-specific toxins.

In your case, the power didn't need to go out. There just was so much gunk that probably a little section went anaerobic and started releasing toxins that started killing other bacteria in the canister. Finally, the entire ecosystem in the canister crashed, as in a "meltdown."

I hope you have some fish left.


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## s2man (Nov 8, 2016)

Wow, what a mystery. Very interesting and worth remembering.


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