Water Changes

[MCA]

I agree. All too often well water can have CO2 or other gases in it. At the minimum, run the water through a degassing tower. Better still might indeed be to put the well water in large tanks and constantly aerate it.

[yerrag]

Some put activated carbon (AC) in areas of high water flow, as is your suggestion yerrag. But AC is a molecular sieve (as is zeolite) and I have always thought water has to pass through the AC under pressure. Many aquarists do the same - AC in a filter bag placed in an area of high flow. But molecular sieves are not 'magnets', they are sieves. They trap molecules of certain sizes the same way a sand filter traps debris. Or maybe AC just works better in a pressurized system, but still works okay otherwise. Any experts in the area ...?

As for granule size, I believe the key is surface area. Fine granules have a larger total surface area given a fixed volume of AC is used. But the trick is in containing the AC in your drum, yerrag. I have found that small granules are more likely to float to the surface and escape the container (drum in your case), unless the flow rate is really slow.

I believe channeling is better managed with carbon blocks, compared to granular AC. AC Reactors (in addition to being pressurized canisters) incorporate baffles that counter the problem of channeling. AC is not a floating media, so the tried and tested aeration technique is not going to help with channeling. You could end up with a screen at the top of the drum with small enough mesh to keep the AC in the drum and then use water flow rate to mix up the AC so you do not have channeling issues.

You make very good points. The AC block filter is a compact solution, but more costly. In tight spaces, there would be no other option. If space is no problem, a drum with AC pellets would work. Would have to make sure water goes into the inner section of a toroidal cylinder and come out thru the sides of the cylinder, passing thru the AC pellets. The inner tube and outer tube of the cylinder would have to be screens fine enough to keep the AC pellets from going through.

[Jacques]

To anyone interested in using activated carbon (AC) to strip out chlorine, know that not all AC types are equally suited for this task. Coconut based AC is recommended for chlorine trapping while coal based AC is not. Check with your supplier.

Or better yet, test chlorine concentrations before and after flowing water through the AC.

[Jacques]

Which is better ... given the same stocking level, feeding rate and amount of fresh water added each week, a small or large pond?

We all have fresh water constraints, be it $$$, how to dump the purged water, water restrictions, etc.

Say I can manage to add 4 000 gallons of fresh water per week and I have the option to increase water volume from 16 000 gallons to 20 000 gallons. Should I do it?

I cannot increase the pond size (which is a good thing as I may be tempted to add more Koi) but I can increase the volume of my filter chambers.

On a 16 000 gallon pond my 4 000 gallon water change equates to 25%. If I increase total pond volume to 20 000 gallons, the 4 000 gallon water change is only 20%. On a larger pond the water change has a smaller impact. BUT, more water means pollutants are in smaller concentrations.

I ended up with a small spreadsheet model to calculate the dilution effect given the two scenarios and, based on this, I should have the smaller water volume. Only thing is, it is completely counter intuitive! We are brainwashed into thinking more water is better.

I need a different perspective ... Anyone able to help?

[MCA]

Say I can manage to add 4 000 gallons of fresh water per week and I have the option to increase water volume from 16 000 gallons to 20 000 gallons. Should I do it?

To me the question is not clear. By "add 4,000 gallons per week" do you mean changing out 4,000 gallons per week? What do you mean by increasing water volume? Are you adding volume to the pond? If the water quality is OK, I can not seen any value in increasing the size of any filter chambers. If I wanted more bio conversion surface area, I would be adding a shower. With a shower you get aeration and nitrification. With some types of media, such as BHM, you may also get some denitrification/ mineralization.

[sacicu]

More water or less koi to water would always be better as the dilution of pollution is better while the allowance for mistakes is bigger.

However each case is different. If you increase filter size but makes it harder for you to clean it then the additional water volume might even be counterproductive to your intentions of the solution of pollution is dillution.

[Jacques]

Thank you for your input gentlemen. Let me clarify:

I am going to build a concrete irrigation reservoir next to the pond. When I do water changes, the purged water will be collected in this irrigation reservoir and used for irrigation. This reservoir is NOT part of the Koi pond. Having this reservoir allows me to add fresh water to the pond (water that otherwise would have been used for irrigation) while 'old' water from the pond is instead used for irrigation.

The benefits of having the irrigation reservoir are:
- much higher % water changes during periods of heavy irrigation
- water removed from the pond during water changes, are not just dumped at the back of the yard but instead gets used well

At a comparably small additional cost, I can also build an additional concrete 'filter' chamber next to the pond. This 'filter' chamber IS part of the circulated system (ie water leaves the pond, goes through the existing filter chambers and into this new 'filter' chamber before returning to the pond). This 'filter' chamber will be empty other than for water flowing through it. No man-made filtration happening here. Its only purpose is that of adding more water to the system and more water means that pollutants are in lower concentrations (and more allowance for mistakes - sacicu).

I am NOT increasing the size of water changes (it remains at approx 4,000 gallons per week). The only time I will do water changes larger than 4,000 gallons per week is when irrigation demand is more than 4,000 gallons per week.

My dilemma is this:
Intuitively it makes sense to have a larger body of water and I should therefore build this additional chamber. BUT, a 4,000 gallon water change in a 16,000 gallon pond (existing size) is more effective at diluting pollutants than is a 4,000 gallon water change in a 20,000 gallon pond (existing pond setup + the additional chamber).

Adding the additional chamber means more water in the system but water changes (as a percentage) are smaller.

[yerrag]

Jacques, it is a lot of work to add an irrigation pond just to be able to use the pond water to irrigate. Costly as well. I also use my pond water to irrigate. But I draw water from the after-mechanical filtration stage, where there is plenty of ammonia, using a centrifugal pump that's connected to the garden water pipes. So that my pump, which has a small gallon-size pressure tank, does not keep cycling, I have attached a cycle stop valve so that while water is being used for irrigation, the pump will not turn on and off endlessly. This uses a lot of electricity and causes a lot of wear and tear on the pump. Annoying as well.

I also have a level sensor placed in my settlement chamber (water surface has to be calm to keep the sensor from giving fluctuating in and off signals), and the sensor controls a water valve that refills the pond.

It works pretty well. I've had this setup for close to a year already and I'm happy with it. I also don't have to contend with mosquitoes, which an irrigation pond may foster.

[Jacques]

Thank you for your input yerrag. I forgot about mosquitoes!

These are the reasons for considering the irrigation tank:

1. I cannot pump 15 000 liters (4 000 gallons) from the pond without dropping water level significantly and causing (IMO) stress for the fish. I can schedule irrigation through-out the week but would need 15 000 liters at least one day out of 7.
2. I want a daytime flow-through of fresh water and the only way to do that is for the freshwater inflow to push pond water over the overflow and into the irrigation tank. This way I can justify adding far more fresh water than what would otherwise be possible.

My project is still in the planning stage and I appreciate the different points of view.

[Jacques]

...a lot of work to add an irrigation pond just to be able to use the pond water to irrigate. Costly as well.

I am not one to throw around money but seeing that the pond is built on a slope I would need very little excavation. Absent earthworks, the bricks and mortar is not going to add up to that much. I hope your experience does not prove my budget calculation wrong