Backyard Aquaponics
A place to discuss aquaponics

The more you read on the forum the more you hear people say that it is best to turn over your water within the fish tank once every hour. I have been running the school system on 15 min on 45 min off using an ebara optima that is rated at 150lpm at 2 metres head. Our head is zero so I assume our pump is pumping at capacity. This would mean it is pumping around 2250 litres in the 15 minutes - less than half of our tank capacity of 5000 litres every hour.

The fact that we have another algal bloom happening and there are only 16 barra, 3 big goldfish and 3 big marron in the tank and the system is well and truely cycled and the 6 beds have plenty of growth in them has got me thinking about water turnover.

Can anyone see benefit to running the pump 30 minutes on 45 minutes off or 30 minutes on 30 minutes off to increase the water circulation or should I just stick with 15 and 45? Can anyone foresee a problem with this and which of the above options do they think would be the best?

Cheers,
Mike

I am currently running my 2 bed system at 30mins on and 30min off during the day and 15min on and 30min off at night.

My water has never been clearer. If this is a contributing factor I dont know. But its giving my plants a break during the hot day and seems to be going really well.

Mike, just my thoughts/logic;

algal bloom means excess nitrates ( I know you already know this ) and you say the plants are having good growth, which means they are probably not likely to significantly decrease the nitrate level further. Extra turnover then is not really going to change anything is it as the bacteria are not removing the nitrates, only the plants are.

Also (correct me if I'm wrong) you have only 6 x 300L of filtration which is way less than 1:1 let alone Joel's recommended 2:1

To my mind, that leaves you two options;

- more GBs/plants
- water changes

Is my logic flawed somewhere ?

Grow beds are 500 litres so we have 3000 litres of filtration, with low stocking the GB filtration is more than adequate. Although we have a 5000L tank we keep stocking way below what the tank could handle. Nitrates are currently 0 or close to so GB's are coping well.

I know the bloom is due to increased light and temp change (tank is in full sun with 3/4 of it covered with core flute) and that increasing time in the GB's is likely to make little if any difference but it just got me thinking about actual water turn over and the statement by many that turning water volume over once an hour is optimal. I doubt it will make any difference to the current bloom, time and no food will fix that.

In smaller (3000 litre) BYAP systems 15/45 would give close to if not 100% turnover with an optima pump but 1/2 hour is needed to turn ours over. Was just hpoing that there may be others who have played around with different times and may have noticed some water clarity differences. I don't want to bother playing with it if others already have and have seen no difference.

Fair enough.

Just for the record, I use 6 x 300 L of filtration as Rupe is always preaching that we should only count the volume of the filter (the hydroton in this case) which is about 60% of the 500L GB.

Are we sure that water flow has no effect on algae?

In both of my systems I have constant flow (of between 1 and 1.5 times tank per hr), and have frequently had nitrates still over 80 when plants are young or recently pulled out. I have never had an algal bloom. Only partial shade 50% on the systems.

The water turn over thing is a bit of a problem for me as follows:

When running on a timer lots of people talk about running for 15 minutes on 45 minutes off. So if I have 2000 litres of water and 4000 litres of grow beds (2:1 ratio) then I need to pump that 2000 litres in the 15 minutes.

My grow beds will not hold 2000 litres of water (1,600 litres probably). But if the grow beds are supposed to drain completely in 45 minutes, some 600 odd litres of water should be going out of the drain holes as well during the 15 minutes helping me turn over the tank volume in the alloted time. Simply put a 2:1 ratio makes 15 on 45 off a reasonable timing.

If I only have a 1:1 ratio (800 litres of water in my growbeds) then it just doesn't work, I need to have a lot of overflow after the growbed is flooded to achieve a full tank exchange each hour.

FF, overflow still filters solids out of the water and aerates so I see nothing wrong with overflow, I doubt that anyone who is running Joel's style of flood and drain does so without any overflow by then end of or even halfway through the 15 min pumping time.

Novaris, I can't say for certain that water turn over has no effect on algal blooms, it is just my gut feel that it would not stop one if the external conditions such as light and temp are right.

Joel or Faye, if you are around, have you guys noticed any difference in water clarity with larger FT six bed systems that may only turn over 50% of the FT within the 15 minute pumping cycle? I would be interested to know what your take on water turnover is.

Cheers,
Mike

More turnover with a sensible amount of growbeds = clean water.

You can only put so much water through a growbed per day, before it is unable to process any extra waste.

Mike I have a 15 min 45min cycle with an Ebara with minimal head on 3000L FT and 800L ST. My full flood happens in about 5 min, so 6 GB hold about 1/3 of the FT (ie the FT is 2/3 full on full flood) so the other 10 min of full flood must circulate about the full tank ever hour. My water is so dark and has been for 3 weeks or so that I can't see jack shite.

I have 50% shade over the whole system and 50% shade over each tank. One would assume that this would be the same as 75 % over the tanks, and I still have lots of algae. this happened before I took all the trout out with a full vegy load. Now with no trout (I think!) and 150 small SP the plants are suffering from lack of nutes and I now have some relativly empty beds.

In the last week I have thrown a blue poly tarp over the FT and another shad cloth 75% over the ST and no results yet.

Rick, you are going through the first season algea dyeoff. You get them at change of season from cold to hot and from hot to cold in autumn. It happens when your water temp starts to exceed around 20 degrees.

Nothing in my system has changed, and I have not had one this year. But I did for the first 3 season changes.

OBO, what you describe Rick as having is what I figured we had as it has only happened since the water exceeded 20 degrees.

Rick we have pretty much the same system but with a 5000 litre FT in place of your 3000 litre one. We have been running less fish than you and most others with six bed systems though. I was wondering whether there is any benefit to running the pump longer so that the rest of our tank gets the benefit of being overflowed through the GB's?

Only up to a certain point - the growbeds will only catch a certain amount of the dead algae each cycle.

If you look closely at your tank walls, you'll see that black algae is peeling off, and green algae is growing in its place.

Say we assume the algae is not a problem. How important is it in any system to turn over 100% of water per hour, it is often sprouted as what should be done but is it necesary?

After typing that I am thinking stupid question Burnsy, it is all related to fish load, grow bed capacity, plant density so every system will be different.

That said, has anyone had any negative effects or comments to make about leaving beds drained for a shorter period than 45min? Will I get root rot problems if I trial 15/30?

Algae can sometimes be something of a mystery where one person has it no matter what they do and another might never have a problem with it even though they are doing everything wrong according to the "logic."

However, the note about tank turn over. I do believe having a 2:1 ratio and turning the fish tank over at least once per hour works quite well. Now if you have a 1:1 ratio and let the beds overflow longer to get the full tank turn over each hour, it will greatly improve things (or if you can arrange your stand pipes such that it takes 15 minutes to fill and then they can drain in 15 minutes so you could do 15 on 15-30 off and so on but that could get tricky depending on the pump. (my beds can fill in 15 minutes and there are lots of fairly big holes in the bottoms of the stand pipes so they drain in about 20 minutes so lots of water flows through them during a cycle.) I do agree that there is only so much water that can be put through a grow bed each hour though.

I have run systems with 15 on 15 off. So long as the beds drain enough, it can be fine (though that will depend a bit on the solids load from the system and the plants being grown.)

And the limits of the grow beds are a big issue for those I know are running something of a swimming pool with only a small amount of grow beds. Those systems usually need some additional alternate filtering to keep the water nice.

I do think adequate water turn over is a big step to improving water quality if problems are apparent.