Hydra in Daphnia tanks

We are starting two Tilapia ponds and I thought I'd see if I could design a Daphnia cultivation system to work along side them.
A little background: I'm in Thailand, so most days are pretty warm. 55 gal barrels will be shaded, wrapped and irrigated with the overflow from the 2 gal regulating bucket to cool. (suggested after diagram was drawn)

The intent is that this is virtually self sustaining and low maintenance.
A percent will be harvested every week as a treat for the pond fish, the indoor aquariums, and to keep system from crashing.
Constant green water supply from the ponds means less chance for ph, or ammonia build-up.
Additional feeding to Infusoria Tank upon harvest, if deemed necessary.
Quarterly siphoning of detritus and search for eggs.

I would appreciate it if someone with more knowledge than I, could take a look at the diagram and see if there is anything I have missed.

My Concerns:
Providing green water from a natural source is prone to introduce unwanted visitors. My main concern being Hydra.
I can put Snails in to control the Hydra, but I have heard that Scuds, another unwanted guest, have a fancy for Snails. (Ordinarily, I would not care, but they eat the thing that eats the Hydra, so back to square one)
I've also heard conflicting reports that Assassin Snails will eat both Hydra, and Scuds, but are difficult to breed. Buying enough Assassin Snails year, over year, is not an option.

What, if anything other than manual removal, can control Hydra in this situation? Or am I being overly cautious?

-sterling

In my Canadian experience, hydra and daphnia cultures go together like young love and heartbreak. I don't know if anyone has ever been able to have one without the other. It doesn't mean serious losses to hydra though. They colonies go wild on artemia in a closed system, but daphnia with a greenwater flow will probably be okay. I would always see a few hydra in my culture tubs, but never enough to be concerned.

It's like mosquitoes - a few always get in with screening, but only a few.

Interesting! GaryE knows more about this than I do. I will say that assassin snails will reproduce quite easily and their population will rise to the level of available prey. I introduced three (only three) into a 12 gallon tank with a serious trumpet snail problem, and within about six months I had a dozen assassins and no trumpet snails!

I have never kept assassins. I bought a couple once but they didn't last long. But any snail I have bought to kill hydra hasn't killed hydra.

have the daphnia/ moina cultures separate from the other containers. If the pond water quality deteriorates, it will kill the daphnia. You will need to start new cultures regularly because they just about always crash after a few months.

if you put the daphnia/ moina into an aquarium and monitor them for a few days, you should be able to see if there's any hydra in there and if there is, it should have attacked itself to the glass or substrate. Then you just scoop out the daphnia and put them in the pond and flush and dry the tank.

GaryE said:

I have never kept assassins. I bought a couple once but they didn't last long. But any snail I have bought to kill hydra hasn't killed hydra.

Click to expand...

As I understand, not every snail will eat Hydra. 'Pond' snails are supposed to, but that sounds like just a generic term to me.

The Thailand (actually an invasive species from South America) Apple Snail, and/or Golden Snail will eat Hydra. They are literally everywhere here, and I crunch dry shells just walking everyday. Rice farmers have big parties and invite locals for snail gathering parties to get rid of them. (Look at that 'S' Car Go)

Ideally, I would like to find something that eats scuds, but leaves the daphnia alone. Even if that thing would normally eat the fish in a normal aquarium. Have given up looking.

Question 1: As I am concerned that scuds will eat the snails that I use to control the Hydra, will scuds bother Apple Snails that reach larger sizes? No worries in the wild, but this being a closed system changes the dynamic.

Questions 2: Although you can eat the Apple Snail, their eggs are toxic to human touch, and will kill mice. How concerned should I be if a snail lays eggs in the system? Will the toxins kill the daphnia? The snails like to lay above the waterline, but there won't be much above the water in this system. ...or will the constant water flow prevent toxic build-up?

Question 3: Just for fun, as this last is not really a concern. How big a snail will an Assassin attack? A snail the size of a peach is not uncommon. Note that I've only seen a shell the size of the big one in the pic below once.

-sterling

In my experience assassin snails won't attack things much bigger than themselves. I've heard they will gang up on apple snails and kill them, but I've never seen it happen.
Holy smoke, that las tone is HUGE! I've never seen one half that big.
I've had them lay eggs on the lid of a stocked fish tank, and didn't notice any toxicity issues. I had no idea their eggs were toxic. I've never eaten a snail, because frankly I've never been that hungry.

There are many species of Hydra and Daphnia, but they all stay within general patterns. I get Hydra of different sizes, different danger levels to fry, different colours, etc, and that is within one fishroom in Canada. It's probably safe to guess your hydra and daphnia are similar. After that, all bets are off. I don't know your fauna and could easily miss on any help I tried to offer.
I don't imagine you have the same concerns with outdoor cultures attracting raccoons, thirsty deer or bears, right?
I'll wish you luck in the project, but hope someone who knows your environment better can offer more concrete experience.