Backyard Aquaponics
A place to discuss aquaponics

Calcium is amply supplied by all the calcium carbonate in the shells in my system. In the other system that doesn't have shells I add lime or chicken grit at the inlets to the grow beds to keep the pH above 6.5.

As to Iron and potassium. I use a powdered chelated Iron product that I add a spoon full under the water inlet of the grow beds every few weeks or when I see signs of deficiency. Keep in mind that my grow beds are each 100 gallons so for your system you would need a really really tiny spoon, or better yet just a pinch to each grow bed or perhaps a 1/4 tsp for your hole system every couple months or so.
The potassium I use a seaweed extract. Here I use Maxicrop many others will use seasol. Just make sure to get a seaweed extract that doesn't have any added nitrogen or phosphorus as that would overload the system. I just add a splash at the inlet to the grow beds. For my big system I might use a quart total but I don't tend to add it as often anymore. Once a system gets mature it might not be necessary to add much of anything provided the fish feed is high quality and the pH is kept in an appropriate range.

What do you think about the practicality of adding iron via rusting screw ties, a couple of nuts and a protector grill, potassium through bananas in the ST and calcium through egg shells in the ST? Would it work...?

Also, seaweed extract, any seaweed extract without nitrogen phosphorous and that is non toxic will work yea, that a local spa or natural/organic products store can supply?

I'm not sure that simply adding metal bits will actually provide iron is a plant usable form and there is always the danger that there might be other metals than iron mixed in that could become toxic to the fish and even the people eating them and the plants. You need to make sure any metal added for the iron doesn't have copper/zinc/nickle/chrome/led/ and probably a few others. Kinda hard to assure that with old rusty bits.

However, some people have put metal into systems for the iron but I don't know how successful it was. Look up the "conversations with a Really Smart Guy" thread
http://www.backyardaquaponics.com/forum/viewtopic.php?f=8&t=1523&hilit=conversations+with+a+really+smart+guy
It has some ways that might actually turn some iron bits into something plant usable if you want to try it.

Seaweed extract like you get in liquid form from a garden center is what you want. The fertilizer numbers on the Maxicrop say 0.1-0-1 for the nitrogen-phosphorus-potassium numbers. (avoid anything with high amounts of nitrogen or added fish emulsion since you already have fish in the system.) I'm not sure what type of seaweed extract you get from a spa or health food store.

Banana peals, well if you are fairly certain that they are not heavily covered in pesticides, they might not hurt but I don't know how much they actually help either. Before I managed to get my hands on the seaweed extract I did bury some bananas (banana and peal cut in half) in my grow beds but I don't know that it did much other than feed my worms but if you have nothing else.....)

Egg shells, well if they are well washed out (cause any egg remaining in them would add to the bio load) they could be added like you would add shell grit, however, you would have to have a lot of egg shells to really do the job. You really need a pH test kit so you can keep track of that at least. If you have enough buffer in your system to keep the pH at an appropriate level, then you will likely have enough calcium. Some grit like people give to chickens is a really easy way to add the buffer and provide calcium. Yea egg shells would qualify but in a tiny system you don't want to add extra bio load while trying to balance pH or add calcium and I don't know how much you really want to be washing out the egg shells (I usually crush up egg shells to put in the worm bins so it isn't like I'm wasting them.) A hand full of lime stone chips or chicken grit under the inlet to the grow beds when ever the pH is getting below 6.5 seems to take care of my pH and the calcium requirements.

Many people use potassium bicarbonate to keep pH up while also providing potassium, that is a product that many beer and wine making shops may carry if those types of things are easier to come by in your area.

potassium bicarbonate sounds like a good idea, will work on that in the morning.

Also, your mention of the shell grit gives me an idea, I can just chuck in some of the gravel that I earlier got and tested to have limestone in it, that ought to buffer it and add calcium! A bunch of them in the ST or in the GB under the water inlet should do the trick I think, thanks TCL

There ya go, ya got the idea now.

The cheapest source of potassium I've found around here is potassium chloride in 40lb (about 18kg) sacks for use in water softeners. Normally about $25, I saw it for about $14 at Costco last week. Of course, that would supply all you would need for a family garden for years and years...

Or you can get the little bag of murate of potash from the garden center (murate of potash is potassium chloride) Strong stuff so ya don't need to much.

potassium chloride? wouldn't the chloride part of that be bad, very very bad...?

Hi TCL, had a bit of a ph scare when i topped up 500ltrs from the tank but forget the hose and ended up putting 1000ltrs in - my water tank has got acidic water in it and i didnt realise. Followed your tip on garden lime and shell grit over the last week and itrseems to be stable at 6.6. Hoping it will come up slowly with the shell git in the SLO filter....Melbourne must have acid rain!
Ben

Rain generally should be a bit on the acidic side naturally and it doesn't come with any buffers in it the way well water often does. Adding some lime is a good idea when using rain water for a system, just don't add so much that you wind up with a pH over 7.6.

Chloride in small amounts is not bad. Ya know when we talk about salting a system to help mitigate nitrite toxicity, it is actually the chloride from the sodium chloride that takes care of that.
Chloride is not necessarily the same as chlorine but I didn't finish chemistry in school so I don't know the fine details there. Rupert seems to know a fair bit of the chemistry stuff though.

And when using potassium chloride, you only use a tiny bit since it is a huge source of potassium. The Murate of Potash shows the fertilizer numbers being like 0-0-60 I think. When you concider that when you salt a system you are usually going for parts per thousand, salting a system will add way more chloride than going for something in the range of parts per million of potassium. (Potassium is generally needed in lesser quantity than nitrates and most of us try to keep those under 100 ppm just to keep them readable.)

Been busy lately and not online too much but I'm still here and the AP systems are still chugging along. Netted out a 5 lb catfish for dinner yesterday, Dang way to big for a meal for just two of us.

Had a bit of a problem with my home made automated low pressure valve. A little plastic bit of the flapper broke and the valve wasn't closing properly part of the time which would leave water flowing through the indexing valve so it wouldn't always index forward according to the program. So, Since I can't get the part to fix my automated valve this weekend and it will be a week till I can get the part and fix things, I've made an adjustment that could turn out to be a handy adaptation to those who might wish to switch from indexing valve operation to constant flood for say cool weather.

I've removed the stem disk assembly from my indexing valve on the big system so now when I send flow to the valve, it flows out all ports. Then I went and flipped the stand pipes over to set the grow beds for constant flood and did a bit of tweaking to balance the flow to each bed a bit. Tada, constant flood system!

I had to add quite a bit of top up water to the system with all the beds being flooded but that is fine, system is heavily stocked at the moment so the constant flood is kinda a good thing. (now the entire system isn't constant flood but well over half of it is.)

So I'll be able to share how the plants do with over a week of constant flood since I took some pictures today and I'll take more again in a week or so.

This constant flooded comparison will be most intriguing!

As creative1 has found, constant flood can work provided you have enough grow beds and the flow rate through the beds is sufficient to keep the aeration high.

It may also partially depend on the population of root rot organisms or a number of other factors. The UVI test on basil found that they lost more and more plants to it as the experiment progressed and the problematic organisms built up.

Definitely some plants do poorly when the crown stays too wet. And yes, certain plant diseases will build up in a tropical system. Luckily I'm in the sub tropics so some of those diseases will naturally be set back through the winter. I don't intend to leave that much of my system constant flood long term, only until I can get the parts to re-build my automated valve, so hopefully a week or two won't be long enough for those nasties to build up and do damage.

I do think that switching a system to constant flood like this might be a handy way to keep water temps up a little bit through cold weather for warm water fish and on the flip, keep water temps a bit cooler for trout through extreme hot weather seeing as the flood and drain action through grow beds is such a good heat exchanger. Switching to constant flood also adds a large amount of extra water to the system while running that way.


On another note, the water chestnut experiment seems to be showing the bottle cap bin to have the best plant growth on a quick glance. Still growing lots of algae but not it's green string algae instead of the brown stuff and my system pH is holding at a nice 7.2 the last several times I tested it.