Backyard Aquaponics
A place to discuss aquaponics

As you probably know - Murray has one bed running flood and drain with coco peat as the medium.

Hello Hayden;
I will google coir. First I have heard of it.
I have concerns about pythium and most people at the forum are doing well with flood and drain. The grow beds I am building are strong enough for pea gravel if I end up in that direction. Also, the computer and pumps can provide flood and drain. I will give DFT a try this year, but next year I may be converted to red worms and gravel. I will be most interested in your results.

For the most part it all depends on the intent of the system.
For systems of the scale we are looking at, pea gravel beds should not be a problem at all.
Dr. Savidov's concern is that in intensive culture of fish solid wastes will be more than the gravel beds can handle, and would require frequent cleaning...obviously a very labour intensive process. However if there are not huge volumes of sediment from intensive aquaculture, then a gravel bed with worms will suffice. Likewise, with frequent removal of plants, there is bound to be some feeder roots left behind. Can worms effectively deal with this? We shall see.
An advantage of coir is that say in a growbed scenario, it could be used for a duration of time, then removed and placed in a bin with redworms, thereby recycling the coir to be used again. This has a limited repeated capability but coir is very cheap.

As I stated, I am interested in refining the process of using redworms to break down solids in gravel, making it more feasible for commercial application. We shall see what can be varied here.
There are commercial gravel bed systems that are successful, it all depends on management.

Using more efficient clarifiers may solve this issue as well.

Hi,

One of the issues that has been canvassed with gravel beds is that they can eventually clog up due to the accumulation of fish wastes.

EB has had a number of beds that have operated for several years without showing signs of clogging so it must be a question of which operating system you use and how well you manage it.

For those who have such concerns, I'd be inclined to consider using expanded clay aggregate (or perlite in smaller systems) with gravel on top......to weigh the clay balls/perlite down so that it doesn't float.

When it comes time to renovate the bed, you scrape the layer of gravel off and then fill the grow bed with water. Stir up the media and the clay balls or perlite will float to the top where they can be easily recovered and cleaned.

What remains in the bottom will be fish waste, plant roots and a bit of gravel that remained in the bed after the scraping operation.....easy to separate out.

Gary

A system which I always forget to integrate into my growbeds, and realise after they are full with gravel is to include a cleaning setup. My previous biofilters used a grid of small diameter PVC tubing which sat in the bottom of the container. The plan was I would periodically pump a fair amount of compressed air into this tubing, breaking up solids in the filter and allowing them to filter out or using the drain tap I could emty the filter out.

Another concept which I did use this time round in my current growbeds, was to use broken terracotta pots (smallish peices) in the very bottom of the growbed. This lower density may reduce the clogging of large particles and will allow better water movment.

Gary, indeed, Dr. Savidov has not demonstrated that this occurs in gravel beds because he does not use gravel beds. He has simply eluded to me in conversations that he believes in intensive operations, both fish waste sediment and plant debris may build up providing a food source for pythium. In their work at the CDC they have gone through periods of pythium infection, loosing plants. They found that proper management and prompt removal of infected plants to be key. They also employ a pool floor cleaner to clean the floors of the DFT channels, a great time saver.
He does not discredit gravel beds at all, he just sees the labour involved.

The issue is not clogging at all.

With that said, the clay balls layered with gravel is definitely another solution worth concidering. The only issue is the cost, but if that can be balanced by reduced cost in labour hours then it is positive.
Who here has tried this method?

Most clay balls will not float after being imersed in water for a reasonable period of time.

You may be interested guys that when doing a bit of harvesting from my gravel bed yesterday, I decided to did a big hole in the part of the bed that had become vacant to see if I could see any compost worms (which is what I think you refer to as redworms). Found plenty - including a couple of woppers in breeding mode. This is good - because I only put a few in the system - so it is clear that they are doing well and multiplying. When the number get higher I expect to see a difference in the way my system performs - not that is is not doing well now :-).

I see them occaisionally come to the surface in the evenings.
I assume they are just saying hello

I use Ubuntu. Is that subject to clogging?

Hi Raimuiso,

I must have been sniffing pixie dust when I made my last post on this thread........and I've edited it accordingly.

While I've heard that clay balls will no longer float when they have been in water for a while, this hasn't been my experience. It might come down to a particular brand.

In any case, if you leave the bed to dry out for a few days (after the gravel has been removed), they will almost certainly float.

NJH.......you're getting worse, but keep at it.

Gary

Perhaps a layer of coir laid upon the clay balls might provide an excellent labour/functionality situation. Wet coir would definitaly weigh the clay down, along with its own benefits of resisting pathogenic lifeforms and uniform moisture.

Hayden

[font=Times New Roman] [/font] Today I built part of the heat exchanger. The pictures show the 6 ten foot 1/2" copper pipes and union couplers at the ends and the air bleed that will be at the highest point. These pictures are before the flat black stove paint is put on the pipe. I thought the photo after black would be poor. This whole unti gets mounted at the top of my glazing in full sun.

We will see how much heating I get. The pump is a 50 watt 12 volt pump at floor level. Then the exchanger in the fish tank is below ground level. The expansion tank will be at the pump. With the air bleed at the highest point in the system, I think all will circulate nicely. The pump is controlled by my embedded controller computer with info from temp sensors at both exchangers, the fish tank, the inside air temp and the outside air temp.

[font=Times New Roman] [/font] Here are a few pics of my greenhouse I just took.
It is very messy. I am working on the vent opener, the heat exchanger, and doing trim and painting. Cleanup has been put off for a while.

[font=Times New Roman] [/font] The front(South) knee wall has 11 vents (24"x14") hinged at the top. They are lifted by arms on a 32' drive shaft of 3/4" galv pipe. The drive shaft is rotated by a 16" dia pulley. The pulley is belt driven by a 12volt motor. I just found that the motor can not handle the torque required. I found a 10:1 gear reducer on e-bay and it is on its way to solve my problem. Here is a picture of the vent lifter.

Soon to be a very suave greenhouse....
What type of paint will your tank exchanger be painted with?

Hayden