adding a grow bed as fish get bigger

[RW]

I have a 120 gallon tank with two planned 2 ft x 3 ft x 1 ft deep grow beds.

I was originally planning on putting both grow beds online at the sametime, but then a thought occurred to me... Would it be better to just have one grow bed for now, and then as the fish get bigger add the second grow bed? 

 

[Lonny Harper]

Will it be harder to add the plumbing after the fact?  Would it affect cycling?

[Kobus Jooste]

There are a number of ways in approaching a system with the initial lower fish biomass typical of newly installed units.  As long as the design is properly scaled to deal with your maximum expected fish biomass, I also do not see much of a difference in these approaches.  The scaling ratios I use originated from commercial research units that had multiple fish tanks and rotational harvests, which meant that once up and going, it was always pretty close to maximum fish biomass.  In a small home system, you typically start off with a small fish biomass for the first couple of months at least, which gives you options:

1. Install the complete unit, plant all the beds once cycled and expect slower initial growth.
2. Do as above, but only plant one bed and leave the other one a while to serve only as media.
3. Install all the plumbing connections, but have only one bed in place to begin with, and cycle the new bed a month or so before the biomass of the fish will start posing problems to the single bed.

If a close eye is kept on water quality, I do not personally see a problem with following no.3, but if you are new to aquaponics, having the greater initial volume of grow bed may allow you to make feeding errors or other "learning curve" mishaps without having to stress about the filtering capacity of the unit. 

 

Thus I think the more cautious advice would be to get the whole media volume in there, and you decide whether you plant in both initially or not.  If finances, time or something else is an issue, or if you are experienced with water quality management, plan 3 will also work, but you will have to watch the system more closely and there is a greater risk of something going wrong with water quality. 

[RW]

The plumbing is in place. I'll put both beds online at the sametime and adjust the planting as appropriate to the fish biomass as per your great suggestion. thanks for the help.

[TCLynx]

Good RW, that is the prudent choice.  You can never really have too much filtration.