Water Quality 101

Water quality is a very general term. People at different experience levels have very different definitions. This page is directed at beginner level. I'm only going to cover 3 things, but in detail. Maybe you won't understand very detail but hopefully you will get a sense of that there are some things you don't often hear about. I'd say 95% of pond "experts", sales people in pond stores, landscapers who say they install ponds, people posting thousands of posts in pond forums, neighbors, web sites, pond book authors, all don't know or care to know. The 3 things covered here will cover 90-95% of the things that will keep you fish alive.

The idea is the better the water the less stressed the fish the better their immune system the better they're able to fight off stuff. Their immune system is a keeper's best weapon by far. It most cases problems start with poor water. So even if you cure a sick fish, putting them back into the same poor water would likely not fix the problem.

Step one: Basic understanding of where you're water is now.

That means buying a test kit and testing the water. $10.

What tests? Let's keep it simple. Two basic tests cover amost everything. Ammonia and KH. There are lots of other tests, GH, nitrite, nitrate, pH are common and many more that are less common. These all are more useful at higher levels of fish keeping. Ammonia and KH cover some of the other tests also, so for my money these are the ones to study and do.


Ammonia level is important to know before we do pretty much anything. It can tell us many things and it can mislead us too. Ammonia is about the most likely chemical in the pond to mess us up. It reacts with lots of other things and is harmful to fish. So before adding any chemical we always want to know ammonia level and understand what it means. High ammonia level does not mean fish are automatically in trouble and we should start running around doing stuff. That kills fish faster.

When most people say "ammonia" they think its one thing, but it's actually 2. The test kit most people use is a "Total Ammonia" test, meaning it can't tell the difference between the 2 kinds and just tells you the total. There are charts for figuring out how much of each, more on that later. Lets start with how these 2 ammonias work and why it's important for us to know.

Ammonia is NH3. It is very toxic to fish. Let's just call it toxic ammonia.

Ammonium is NH4+. It is pretty safe for fish. Let's just call it safe ammonium. You almost never hear about this stuff. You now know more about ponds than most "experts". Don't get cocky, it's a pretty low bar.

Couple of weird things about these two. One is that they change back and forth pretty fast and easy as water temp and pH change. Warmer water converts safe ammonium quickly to toxic ammonia. As pH increases safe ammonium converts quickly to toxic ammonia. When temp and/or pH drops the some toxic ammonia converts back to safe ammonium.

I'm sure it's occurring to you that measuring "Total Ammonia" isn't really telling you much. For sure you don't want to freak out if "Total Ammonia" is X. What you care about is toxic level. We can figure that out by using a chart like this great one provided by the Koi and Water Garden Society of Central New York. It's a little tricky but take the time to work thru. At least get a sense of how much temp and pH effect ammonia, what levels are actually a big problem and which levels you have time to deal with in a safe manner.

Why we care about ammonia.

You probably already know, ammonia is toxic to fish and actually other things we care about. Long term exposure stresses fish and many times they die from other casues because of their weakened state. But it will also kill an enitire pond of fish overnight.

We care abount ammonia because anything we add to the pond can react with ammonia, or stress fish more.

Ammonia tells us about our filters. Don't know if your pond even needs filters? Ammonia will tell you. Don't know if your current filters are good enough? Ammonia will tell you. Filters and ammonia are directly related. The only other indicator you have about whether you have enough filtering is dead fish. That's it. It isn't complex at all.

Dealing with ammonia,

Ammonia is produced by fish, mostly from breathing but also from poo and urine. It is also produced by decaying organic stuff liek algae, plants, leaves, dead bacteria and bugs.

Ammonia is removed from the water a couple of different ways. Let's just consider the main 2. You may have heard about bacteria converting it to nirite and then nitrate. That is one way and pretty much all you ever hear about. And in ponds with high fish loads it is the main way. But for backyard Water Gardens the main way ammonia is removed is more likely to be plants, algae for the most part. That's important. A green pond will almost always have zero ammonia and nitrate because the algae sucks it up as fast as fish can produce it. So what happens when our pond clears? Ammonia can suddenly become a problem because the algae isn't consuming the ammonia from fish and the dead algae is decomposing and creating more ammonia.

The bacteria that convert ammonia are everywhere. On your keyboard, in the air, in your pond. There is almost no reason to add bacteria to a pond, it's already there. Given ammonia it will grow. You don't need to have a man made bio filter (that's what we call houses for these bacteria). It grows everywhere. Probably the highest concentration of these bacteria will be on the inside of pipes for most ponds. The question can your pond by itself handle the ammonia being produced in the pond? The answer is always the same, it's not complex...ammonia test will tell you. If you measure near zero ammonia there is no reason to add bio filters. If you measure ammonia it's time to think about bio filters. Most backyard Water Gardens never need a man made bio filter.

But don't be fooled. If we add city water to our pond, at start up, water changes, topping off, and add a dechlorinator we can get mislead by ammonia. Dechlorinator doesn't remove chlorine as much as it converts it to other things, one of which is ammonia. Since ammonia is toxic to fish these products contain other stuff to chemically make ammonia safe for fish. This same type of product can be pruchased on its own, Ammo Lock, etc. Safe ammonia, cool. Problem is the normal ammonia test can't tell the safe from the toxic and those charts are no longer accurate. So you're back to having no idea if you have an ammonia problem or not. There are ways to deal with chlorine that are cheaper and safer and don't get you into this corner. Basically buy a chlorine test kits from a pool supply and wait for zero chlorine before adding fish to a new pond. Trickle water changes allow chlorine to dilute and also react with organics which use it up. Cheaper and safer, what's not to like?

That's the basics of ammonia. I don't really want to get into the full range of bio filters, it's a whole deal. Cross that bridge when you come to it.


Everyone worries about pH. People get pH crazy. Here's the deal, pH is complex. It's hard to measure correctly, it changes throughout the day and in some cases the level is meaningless. So I think it is the worst test beginners can use. It causes nothing but trouble and tells you almost nothing. Testing KH tells you way more including what pH is doing. Way better to know what pH will be tomorrow, next week. We should only care about stable pH, not a specific value. Leave that to more experienced people. It is almost impossible to get a pH in a pond that Koi and Goldfish can't handle as long as the pH stays pretty stable.

KH measures the stuff in the water that will react with acid so the acid doesn't lower pH. We call that a pH buffer because KH stops pH from falling. KH is consumed by acid, so it can fall over time. Lost of things in the pond produce acid plus rain water is an acid.

Good KH level is really simple because a nice thing about KH is it's difficult (almost impossible) for it to be too high. For the beginner lets keep it simple, let's say a good KH level is 200 ppm (different tests have different units of measure, I'm using ppm - parts per million). 120 ppm would be OK, so would 500 ppm. But lets say 200 ppm is a good target. In theory, according to a chemist and serious Koi keeper 10,000 ppm would be the upper range, so don't freak out if yours is over 500 ppm. Freaking out is bad for fish. Higher level fish keepers can talk for hours about what KH level is perfect. That's them, the beginner should first focus on keeping fish alive. So 200 ppm will be our target.

Many people will measure KH and find it's fine, 120-500 ppm. Cool. You're done. The higher the fish load the more KH is used up. In those ponds keepers have to keep testing and raising KH. Most Water Gardens don't have those kinds of fish loads. The main factor is the level of KH in your source water. Most areas have KH levels we like so everytime you add water you add KH. Don't fight KH unless you have to. If your pond is always above say 100 ppm there's not a lot of reason to make it higher, but you can if you like.

Let's say you KH is 20, 40, 60 ppm, even 100, 120, whatever, and you want to raise it to make sure pH stays stable.

How to raise KH. First things first. Water with KH of say 20 ppm will have low pH, or pH that jumps all over the place. Remember ammonia? Lower pH makes ammonia less toxic. We are getting ready to raise KH which will probably raise pH which could convert safe ammonia into toxic ammonia. Are we about to kill our fish? The answer is to test ammonia first and deal with that first. Many things in ponds are related. You don't want to get overly focused on one part of the elephant.

So assuming ammonia is near zero and KH is less than we want...

Baking soda will raise KH. It is cheap, well understood and reacts fast (instantly) to acid which makes it a great buffer. It does make the pH a bit higher than optimal, but many, many high end Koi keepers run their ponds with baking soda. Let's keep it simple, baking soda is a good pH buffer for beginners.

How much to add can be simple or complex. There are calculations that can be done to figure out how much baking soda to add. Let's just stay with simple just add a tablespoon of baking soda. Wait a day and retest KH. The KH level will tell you when to stop. This has more benefits than just raising KH which are even more important. It moves KH and maybe pH slowly which is good for fish. Raising KH from 20 to 300ppm in one go is not good. It gives you experience testing water. You get to see the effect small amounts do to your exact pond. It keeps you form having some giant problem instantly. You and your pond get to know each other.

Safety net time...If you've added say 1/4 to 1/2 of a pound of baking soda and still KH hasn't moved, and you don't have a giant pond, that might be OK, but could be a problem with the test or how you're doing the test. It that point you should do more research and look at the calculations for estimating how much your pond should need to give you an idea. Also, if you have a giant pond a tablespoon a day may be a bit silly so you may want to increase the daily amount.

After a few months you may understand more about your pond, what its KH needs are, how it reacts, and maybe learned more about pH buffering. You will be much more able to adjust KH faster if you like.

Water movement.

Keeping good O2 levels in the pond helps lots of things and it's pretty cheap and easy to do. Like ammonia and KH your pond will probably not have an O2 problem. That's normally a problem for high fish load ponds. Of course 2 Koi in a 100 gal pond is high fish load, so beginners can certainly get into that case. But there is a bottom line here...if you're a beginner and a high fish load there are other things that will kill your fish before low O2. So when I'm talking about O2 here I'm talking about improving fish health, not curing all evils. Good O2 can only do so much.

Unfortunately there isn't a cheap and easy test for O2. But it is easy, and often almost free, to greatly improve O2 assuming you already have a pump. So why not? O2 just does many good things, even keep your pond cleaner, not enough to notice, it's not magic, but good things.

Here's the trick. Many pond experts think ponds need splashing water. Fountain and waterfall are the main devices for this in Water Gardens. It is true this does provide some O2, but that's misleading. Gas exchange happens at the surface, O2 into the water, CO2 out. There doesn't have to be any movement at all for this to happen. The exchange does slow down the deeper you go. In a still pond the water at the bottom will be the lowest O2. Just moving the water enough so water at the bottom moves toward the surface increases gas exchange. Fountains and waterfalls aren't really good at that. But there are ways to direct water from these toward the bottom. That greatly improve gas exchange using the same amount of electric. Simple fix, big reward.

I'll have to give more details on how to do this someday. But here's one tip. Fountains. Instead of pushing water into the air point the pump output toward the pond bottom. That will push a lot more water around and get more low O2 water to the surface for gas exchange. Better O2 throughout the pond than adding 4 more fountains.

If you don't have a waterfall or stream you can consider adding a Trickle Tower. This is just a pile of rocks that you pump water over 24/7. It is that simple.

Now there will be a line of people around the block telling you some other filter is better, and some of them might even be correct, most won't. But for being butt simple and cheap a TT can't be beat for the beginner, not even close. If you want to branch out from there cool, if not cool. Don't worry too much about the size, type of rock (though I'd stay away from coral, limestone and soft rock). Above the water and pump water over the top.

A Trickle Tower's main purpose to to help control ammonia, it's a bio filter. But it can have other benefits like growing string algae and increasing water movement in the pond. A Trickle Tower is just a condensed waterfall or stream, so if you already have those then adding a Trickle Tower probably would do much unless you stil have an ammonia problem.

There's tons of other stuff. But those are the big 3 imo. Ammonia, KH, water movement. Covers maybe 90-95% of good water quality. Maybe a couple of hours of studying to kind of understand the basics, $10 test kit, $2 for baking soda maybe. The key is the learning.

Learning is the key. Unfortunately the world is just chunk full of people lined up to tell you their opinions. Store clerks, web sites, forums, neighbors, family members. 99.9% of all info you run into will be that stuff, opinion made to sound like fact. That makes learning really, really, really hard, almost impossible. Being able to tell the difference is really hard, but worth learning how to do.

First, always assume what you're reading/hearing is complete crap. You will be right almost everytime. Verify everything.

One red flag is hearing "I did this and my pond is great". If you believe this to be useful info you are screwed.

Another red flag is if it sounds too easy. Some things are easy, most have some compexity. Like for example, raising KH. You can read hundreds of web sites that say to add egg shells, plaster of paris, oyster shells, dry wall, limestone or you name it is the best thing ever for stable pH. Science disagrees. It is true acid does effect these things. They will increase and stabilize pH given enough time. So you get a thunderstorm that drops a couple of inches of rain which is say 2.2 pH into your pond then yes, given hours or days the pH of the pond will go back up. In the mean time your pond is experiencing a pH swing, the very thing we're trying to avoid. Those things are just very slow to react. Baking soda is cheap, and a fast buffer, can handle the 2.2 pH rain almost instantly but it isn't as fun as egg shells to talk about. The red flag is if egg shell work then why are all these other things also great pH buffer? If egg shell worked everyone would just use egg shell. But they don't.

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