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I'm worried about gas exchange/oxygenation. Will the fish in my new 5-gallon have enough O2? I have a new Fluval V all-in-one. The way I have the pump setup, there is a great deal of flow through filter, but no visible water movement -- the surface is very still and flat. This is how I want it because I would like to have floating plants. The only real break in the water's surface is the "waterfall" into the filter compartment. For aesthetic and power outlet reasons, I'd rather not run an air stone. Will my fish suffocate? More generally, I've heard conflicting things about what's necessary to have good O2 levels, so I don't really know how to think about this aspect of my tanks. Any good guidance or references would be appreciated. Also, are there any cheapish, reliable-ish tests for dissolved oxygen? Something like a drop checker for O2 would be great.

I thought this relatively new data was really interesting. The USDA, in conjunction with two independent laboratories in New Zealand and Sweden along with three fisheries on the Snake River in Idaho, performed one of the most comprehensive studies on Oxygen deprivation while medicating fish I've seen. The study is vast (almost 400 pages of data!) and examined hundreds of parameters but in this instance, what seemed to hold potential benefits for an aquarist, a portion of the study was on the effects of adding aeration vs supplemental Oxygen to fish tanks during illness, while being medicated and to offset environmental stressors. The objective was to determine if increasing the dissolved Oxygen would raise the efficacy of medicinal treatments and/or improve mortality, as well as to determine if other stress factors shared similar weight in the efficacy of treatment. * In typical aquariums with some exceptions, 7.5PPM-8.5PPM of Oxygen is considered normal and healthy. In this experiment, they stocked rainbow trout (125g avg. weight) into tanks with three different values of dissolved Oxygen.: -Tanks average dissolved Oxygen concentration was at 7.5PPM. Survival and medicinal treatment efficacy were averaged at 88% in the 7.5PPM tanks. -Tanks average dissolved Oxygen concentration was at 6.5PPM. Survival and medicinal treatment efficacy were averaged at 68% in the 6.5PPM tanks. (A third test was done with Oxygen at only 4.5PPM but I've not included that as that level of Oxygen would not normally be present in a home aquarium). Considering that some medications can drop the tank O2 as low as 6PPM (see chart below), the 20% increase in mortality observed with the 6.5PPM tanks certainly underscores the need to keep the O2 high when using medications! They then administered what they considered ‘maximum aeration’. Survival and medicinal treatment efficacies rose, but to a disappointing amount: -Survival and medicinal treatment efficacy were averaged at 93% in the 7.5PPM tanks. -Survival and medicinal treatment efficacy were averaged at 74% in the 6.5PPM tanks. Notice the fish raised in 6.5PPM & 7.5PPM only benefitted about 5%-6% or so from aeration during treatment. That is, the Oxygen levels were essentially fully normalized once aeration was applied. In fact, O2 levels reached complete normality with simple aeration alone. (Their test was taken over a 120-day period). * As above, in a typical aquarium, just simple aeration will almost fully offset these Oxygen losses from some commonly used medications known to suppress dissolved Oxygen. Charted below are six tanks treated with some common medications most of us have used at the default dosages. The O2 level of this water before adding any chemicals was 8.5PPM: The one exception of the medications I've tested being nitrofurazone. Without aeration, it dropped O2 levels to borderline stressor levels (<=7PPM), but simple aeration raises and maintains it to/at 7.5PPM. However, unlike the other popular meds in the graph, O2 levels drop again as soon as aeration is ceased. Unlike all others in this limited test, nitrofurazone keeps the O2 down for at least 48 hours if not more (I only tested up to 48h). Only water changes rectified this. Notice Seachem Prime’s O2 depletion infamy is quite short lived. In just 15 minutes, most of the O2 has normalized and fully so inside of an hour. However, the Prime 5X ‘emergency dose’ drops O2 to near dangerous levels. So, aeration is imperative. Although aggressive aeration brought the O2 to normal levels, it didn’t affect the outcome of medicative stress, recovery or mortality very much. But they weren’t done with this concept. As aeration proved to assist in treatment recovery of only 5%-6%, the Snake River facility partnered with two university laboratories below to test if super saturation of the tanks with Oxygen (hyper-oxidation) would in fact improve the recovery from disease, improve medication tolerance and reduce mortality. HYPEROXIDATION But what if aquarium Oxygen is raised above saturation? If circa 7.5PPM Oxygen is normal and healthy, what effect if any, does hyper-saturation of the aquarium with Oxygen to say, 9PPM or 10PPM have on sick fish being treated with common medications? It's easy to do, but is it worthwhile? Their findings were surprising and potentially valuable to us. A study done by the Universities of Auckland and Gothenburg cites observances of medicated fish with supplemental Oxygen. It was found that an astounding leap in reduced mortality and medicinal treatment efficacy occurs when the tank is flooded with Oxygen. The tank had its Oxygen levels raised above normal Oxygen levels (circa 7.5PPM) and held to 9PPM-10PPM during treatments. Unlike the 5%-6% improvement in illness treatment with aeration alone, once the O2 was temporarily raised to between 9PPM and 10PPM, the outcomes changed dramatically: -Increased metabolism. -It was observed that a small but significant percentage of severely ill fish that were refusing food, began to ingest small amounts of medicated foods after being hyper-oxidated for 24-48 hours. -Improved ability to endure most common stressors. -Improved a fish's temperature tolerance substantially. On average, hyper-oxidation of the tanks reduced mortality during various medicinal treatments by 38%! It also increased the success rate of treatments by the same amount or greater! (Most of the treatments in these tests were deworming's so unfortunately, no data was presented for antibiotic treatments as these fish are raised for human consumption and the USDA limits antibiotic use. However, some of their tests did in fact include “unapproved” antibiotic treatments but the antibiotics used were not specified). The elephant in the room now would be to examine if raising the tanks O2 to hyper-saturation levels would or even could do any harm. To that end, the next observation should be if in fact there are any adverse observations on hyper-oxidation. They list the following as positive to neutral; -Had no effect on fry or juvenile growth. -Insignificant rise in resting metabolism but quickly returns to normal once ceased. -Substantially increases metabolism under stress.* -Increased aerobic capacity and cardiac performance. -Dramatic improvement in temperature variation tolerance. *I'm speculating here but this observation seems to me that it might prove the most important of all these benefits for weak or stressed fishes, especially while being medicated. * An interesting note here. Well into the study is this most odd finding. I wish they provided more information. The statement below is from the study but offers no explanation so I'm simply quoting it here verbatim: "Hyperoxidation of the tanks significantly assists in penetration and kill-off of anaerobic methane pockets, especially in sand and finer gravels." I wish there was more information provided on that one! * With a simple DIY addition, you can hyper-saturate your tank with Oxygen. It may help fish recover from disease and tolerate medications and has no known adverse effects. A simple, Hydrogen Peroxide degassing rig for removing the O2 from peroxide and delivering it to the tank with zero risk of toxicity is linked below. This simply degasses the O2 out of the peroxide and you pump it into the tank with an airstone. If the amounts of peroxide, the bucket size and air pump are used as listed, it will hyper-oxidate your tank to 9PPM-10PPM for two days: Degassing Peroxide Of course, with techniques such as these, you'll never truly know if it helped! But O2 can't hurt (many thanks to @Colu @Gator @dmurray407 @Guppysnail and @OnlyGenusCaps for their input) and a potential 38% improvement in recovery from illness in their tests may make this or some more sophisticated equivalent of this worth trying, especially if you're experiencing fatalities or recovery is slow or incomplete.

Degassing Oxygen from Hydrogen Peroxide I dare say, we’ve all been in a situation where we wished we could increase the O2 levels in a tank. Aside from aeration and lowering temperatures, water changes et al, it’s not all that easy. Testing for O2 is easy: But raising O2 is more difficult. And chances are, if you suspect your fish need oxygen, they probably need oxygen. And extra oxygen can help ailing creatures through unrelated difficulties. One partially successful, but very dangerous method is to add common peroxide as it breaks down into water and O2. Hydrogen peroxide toxicity is dangerous and easily overdosed. In fact, it is this very toxicity that prevents you from being able to use all of the available O2 in peroxide. The maximum amount of O2 available by dosing peroxide directly into the tank is only 1% of the total free O2 available in peroxide! Not unlike degassing Chlorine from tap water, you can degass pure Oxygen from peroxide without risk. The method below will release nearly 100% of the O2 without any toxicity at all. This may present a quick and inexpensive way to temporarily but dramatically increase the oxygen level of a fish tank with 0% chance of toxicity. All one needs is about $10 worth of common hydrogen peroxide, a 5-gallon bucket and a small air pump and stone. The amount of common peroxide (3%), the size of the bucket, and the output of the air pump are married to the following numbers. That is, using these amounts and sizes will produce the amount of O2 specified below. If you need more or less, you simply scale it up or down. You'll need: A typical drug store bottle or hydrogen peroxide, 32 oz is about 0.89c or thereabouts. You'll need 10, 32oz bottles of 3% Hydrogen Peroxide. An aquarium air pump that outputs approximately 0.5 liters/hour. https://www.aquariumcoop.com/collections/all/products/usb-nano-air-pump A 5-gallon Lowes bucket. BTW I say ‘Lowes buckets’ because Home Depot buckets are not airtight, at least not with the default lid, and HD buckets are orange, allowing light through them which breaks down H2O2. Lowes are dark blue but whatever you use, if it's dark, closes and holds 5 gallons, it'll work. Make a hole just large enough for an airline tube in the bucket top. If using a wall powered pump, make one for the power cord as well. Seal around both holes to make it as airtight as possible (I use hot glue). I hung the pump from its cord and tied a knot in the power cord to hold the pump up above the peroxide in the bucket. I’ve opened it to show how simple it is: Add the 10, 32oz bottles of peroxide and close it tightly. Press the top back on and try to make certain it's fully closed. Simply start the air pump for 48 hours of augmented O2. Replace the 10 bottles of H2O2 every 3rd day to resume the same operation and values. This informal rig will output approximately 80% pure O2 for 24 hours, dropping to about 40% pure O2 for the next 24 hours. Finally dropping to circa 25% for the next 24 hours which isn't much different than normal air (normal air is about 21% oxygen). So, it's really an effective O2 generator for the first 48 hours. After 48 hours, you basically have a half-filled bucket of distilled water. ONLY pure oxygen goes into the tank and nearly 100% of the O2 that is available in H2O2, or about 94% greater amounts of O2 than would be possible by adding H2O2 directly to the water. The way it works is the H2O2 has a half-life of 24 hours. 2.5 gallons of 3% peroxide has about 6 gallons by volume of available O2 in it. If the lid is closed, it's enough positive pressure applied to prevent significant oxygen loss. However, once you turn on the air pump, the internal pressure in the bucket goes negative and the H2O2 begins to leach pure O2, leaving behind H2O. The rate of flow of the air pump must be <= than the rate H2O2 releases O2 such that the air pump output should be between 0.3LPM-1LPM or ideally around 0.5 liters/minute. At that rate, the air pump output essentially matches the rate H2O2 leaches O2 so the air pump output will begin outputting 100% pure O2 at Hour-1 but drops to 50% O2 at Hour-24, or a 75% O2 average on Day-1. Day-2 will see the half-life erosion again reducing the O2 from now 50%, to 25% in the next 24-hour period, averaging 37.5% O2 for the second 24 hours. Alternatively, and more potently, you may administer pure O2 with devices like these which of course are more effective and precise at cost of $300: Lastly, I always try to use commonly available items or techniques as in this way, it’s approachable and easily employed as opposed to equipment only a lab may have access to. To that end, you can buy MUCH stronger peroxide in hardware stores. Some 70% vs 3%! If you choose to, that goes much further than 3% bottles from a drug store. Just scale it down by dilution if you use industrial peroxide. It’s very dangerous to handle but it would reduce the operational cost of this no frills “O2 generator” to pennies. But be careful, industrial peroxide is caustic!