Backyard Aquaponics
A place to discuss aquaponics

Couple of points.... optimum to keep your "flood" level to within about 25mm of the top of the gravel to lessen evaporative losses..... maybe a little higher if you need to due to excessive temperatures and/or seed germination... a ball valve on the inlet line will allow some degree of fine tuning/control.

Secondly place your distribution grid/outlet into the tub at the top of the gravel not above it where it will splash, evaporate and/or form an algael slime on the top of the gravel.

Hope we've helped Hunter

Flood and drain times when your system gets established doesent seem to matter in my system now 12 months old all running the same water the outside beds run 3 min on 57 off and the glasshouse 15 min on 45 off both 24-7 the plant growth theres no different except for the temp diff glasshouse slightly better growth [not much]

unless you excessively flood f&f, during my recent spike, I ran the system 24/7 to try and remove more nutrients from the water and it really suffered.

There are so many variables - there will never be a simple answer to this type of question. One reason for running more frequent flood and drain cycles is to ensure that the grow-beds - which are the mechanical and biological filters - are able to filter the tank/pond effectivelly in terms of solids as well as ammonia/nitrite. As Rupe stated, the frequency of flood/drain to turn over the water in the system x number of times will depend upon how much volume of grow-bed you have to volume of tank/pond. The desirable turnover frequency will dpend upon the stocking density and feeding rate of fish.

I personally turn over my 1300 or so litres in my system (sump and fish tank combined) every hour or so. This is done by having a smallish pond pump running continuously, with a bell siphon controlling the flood and drain cycles. When I add more beds - the sycle time for individual beds will be reduced, but I will maintain a similar turnover rate on the tank (or will increase it due to increased fishy stocking density).

One thing to note (although not likely to be a big issue for hunter given current stocking density) is that fish will continue to produce ammonia at night, so turning off the filtration at night can result in build up of ammonia to toxic levels. Also - unless there is suplementary aeration - turning off pumps at night can result in fish death due to lack of oxygen. As I said though - given the size and current stocking density of Hunter's pond - it is not going to be an issue for him at present (more a warning to others).