Sounds like 2 goldies will be fine as long as they are feeder goldfish, also called Comets. Koi goldfish produce much ammonia and the spikes in new water may kill them.
From what I understand, as long as you add new fish gradually, then you will be ok. If you add a bunch of fish all of a sudden, then the ammonia spikes will hurt the fish, possibly kill them, since bacteria colonies must first be able to grow to manage the ammonia.
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Yeah, I have read you can jump start your pond by putting in feeder goldfish, also called Comets. Don't put too many either. The idea behind this is that the feeder goldfish's pookie will provide enough Ammonia to jump start your bacteria colonies and yet not be enough to kill your fish from Ammonia spikes due to bacteria colonies not formed well enough. Feeder fish are also more hardy to live in most kinds of water. Also, fish food and plant decay adds ammonia to the water; so, do not feed the fish too much while you are doing this.
Bacteria colonies form anywhere there is surface area for them to attach. Reason why folk use bio-filters is that bio-filters provide a tremendously huge amount of surface area dependent upon the type of bio-filter media. If you want to noticeably overstock your water, then get a bio-filter. Bio-filters are insanely easy to make if ya know how to glue PVC together and know how to operate a power drill. Check out their DIY section here.
From what I am told, ya don't have to have a filter as long as your water is not overstocked with fish. Fish do reproduce so ya will need to do something to control population such as Haro mentioned with the Kingfisher. Also, I am told Comets will eat each others eggs if you do not feed them much and there are other stuff out there that get the eggs as well.
From reading articles, rule of thumb I found was:
1) a ratio of .5 inches of fish per 10 gallons of water is easy to maintain without bio-filtration;
2) a ratio of 2 inches of fish per 10 gallons will require bio-filtration;
3) a ratio of 4 inches of fish per 10 gallons will require a 55 gallon barrel, or multiple barrels or a fancier unit for bio-filtration.
In other words, for 1000 gallons of water, you can probably get away with 50 inches of fish (10 fish that are 5 inches long) without a bio-filter. If you want to put 80 fish that are each 5 inches long, total of 400 inches of fish, in a 1000 gallons then ya better do water changes and have a 55 gallon barrel bio-filter or maybe even two barrels or something fancier.
Your bio-filtration (bacteria colony size) and maintaining KH will determine if your water is overstocked.
If you want to put alot of fish into your brand new or clean pond, then ya need to cycle it with Ammonium Hydroxide to build up your bacteria colonies. OR ... you could use pre-colonized bio-filter media such as asking a buddy to borrow some of their filter media or get some of their media squeegee liquid.
Learn about pond water chemistry, KH relationship to pH in particular, if you really want to overstock your water. Also, hard water (has high KH) will eventually soften (lower KH) according to the amount of waste your bacteria colonies process. If your KH gets too low, then your pH will have a tendency to crash, meaning all living things in water will die. So, heh, learn more about pond water chemistry, all aspects, if you want to overstock your water and maintain healthy fish at the same time.
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Ammonia? Just plain old household, toxic, stinky ammonia? How much to be safe, without overkill (accidental pun)?
You want Ammonium Hydroxide and zero artificial scents to it and no surfactants. If after shaking the bottle hard and there is a foam built up, then this means a surfactant is present. Chelating agents are safe; this just helps to make the ammonia soluble in water.
The brands I use came from "Do It Best" stores. I have used Blue Ribbon and Z-Force extra strength.
I used one of those small 30mL cups and added 180mL of Blue Ribbon ammonia to my 435 gallon water feature. This brought me up to 5ppm of ammonia to 435 gallons of water.
Product's ammonia content and your particular pond water volume will determine how many mL ya will use to obtain 1ppm of ammonia. All products have varying percent of actual pure ammonia. Ugh, last I remember, Blue Ribbon is 3% pure ammonia.
Remember, this stuff is used to disinfect, or kill, bacteria so do not go crazy. Add a bit, wait a few minutes for your pump to turn over your pond's water once, then test for Ammonia, see where it registers.
Easy to see Ammonia to reach zero on test kits. Takes longer for Nitrites to reach zero. Ammonia and Nitrites are toxic to fish are varying scales.
The bacteria that removes Nitrites is slower to form and is dependent upon your pH and water temperature. I have read it takes 70 F degrees water temperature or higher and 7.5~8.5 pH for optimum growth to form the bacteria that removes Nitrites.
Continue your Ammonium Hydroxide doses each day until the Nitrites reach zero. If you stop the ammonia doses and you do not have fish in the water, then the bacteria will eventually hibernate, or even die off, due to the lack of food for it to consume.
What I did was ... After my last ammonia dose in the morning, I waited until the evening, 12 hours later, to add my fish. This way the ammonia will have had a chance to feed the bacteria and there will be extremely small amount of ammonia remaining once fish are introduce.
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I am noticeably overstocking my little 435 gallon water feature so this is why I jump started my water.
I used the Microbe-Lift regiment, which is, a combo of their PL and Nite-Out and spring/summer enzymes.
I dosed my 435gallon water feature to be around 3~5ppm of Ammonia. I maintained a 3~5ppm to be consumed within 24 hours. Took only a week for my bacteria colonies to get big enough to consume the 3~5ppm of Ammonia within 24 hours.
Next was to wait for the Nitrites to zero out. This took longer for me since my water temperature was hovering between 55 F degrees and 65 F degrees and pH of 8.4.
Took me a little over 2 weeks for my Nitrites to zero out.
You are not completely cycled until your Nitrites are zero within 24 hours.
Take notice, Nitrites and Nitrates are two different things. Ammonia is converted to Nitrite that is converted into Nitrate that is converted to Nitrogen and also feeds plants and algae.
). Right now I'm putting together a PVC pipe support frame that will hold my "false floor" in place. Have 2 baby lilies, awaiting their new home, as well as the turtles who (are they a " who," a "that," or a "which,"....?) are getting very impatient with me.
