Kelp fertilizer

[BK]

Hi all, I set up a 70 gal system less than 8 months ago and have 7 tilapia.  One of them is almost "ready for lunch".  So far we've harvested several tomatoes, lettuce, kale, shiso and such.  Cucumbers and peppers are trying, the plants just aren't producing, peppers are losing leaves and cucumbers develop cukes initially but they whither away.  The leaves on the plant indicate it may be due to a magnesium deficiency.  Today I plan to pick up some epsom salt but was also thinking of a general kelp based fertilizer to help out.  I know it's a new system and has just not had time to mature and develop the mineralization needed to support the more demanding fruiting plants.  The local home depot carries Alaska Pennington 32 oz. Pure Kelp Plant Food.  I would prefer to use something that's more of a known product (seasol or maybe maxigro), but I am new enough to AP that I'll feel better asking advice from folks here that have much more experience.  Even though this sounds like more of a plant topic, the reason I'm asking is that I want to buy/use a product that won't be harmful to the fish, especially since I have added a connected tank with about 250 fry from an unplanned pregnancy.  Advice?

[BK]

Thanks, I have already planted a few more cucumber seeds; along with some squash and eggplant.  With the 3rd unintended birthing of tilapia in my system I'll have plenty of nitrogen to spare.  Once they grow to fingerling size I'll have a decision to make...

I also have 2 plecostomus (algae eaters) in the large tank.  Tilapia will also eat algae since they are omnivores, but generally only if other food sources are not available.  Every now and then I'll catch one snacking on some algae that is growing on one of the terra cotta pot shards I've laid in the bottom of the tank, but without the plecos I'm afraid the algae would get out of hand.  I was worried that there'd be some form of abuse between the fish types but I haven't seen any of that.  The one dominant tilapia is aggressive towards the other tilapia, but leaves both plecos alone.  The larger pleco started off a little smaller than my thumb but after 6-1/2 months in the tank it's about 8 inches long and almost 2 inches in diameter!  Algae must be somewhat nutritious...  Yesterday I added a very small pleco to the fry tank, since algae is really coming on strong in there... a clear tank in full sun for several hours daily.  The fry are visibly gaining size daily.  My wife is showing more interest in the setup than ever before

[Jeff S]

I've had 2 Plecos disappear in my 45 gallon aquarium with 25 3" tilapia in it. The only thing I can come up with is the Tilapia ate them. It doesn't take long for a few hundred fry to dirty up a tank.If you plan to keep any amount of them you better go ahead and start another GB now to handle the load when it hits.

[Kellrae]

Do you add the Epsom salt directly to the grow bed?

[George]

I do, along with everything else I supplement with. 

Kellrae said:

Do you add the Epsom salt directly to the grow bed?

[BK]

I have a separate tank (20gal) that I use to grow duckweed as supplemental (and free) fish food.  This also doubles as something along the lines of a sump.  I add epsom salt to that tank to make sure it gets diluted quite a bit before it gets to the grow beds or fish.  Any other substance (other than crushed oyster shell as a pH buffer) gets added to this tank as well.  The crushed oyster shell gets added to the fry tank since there's more agitation in there.

Kellrae said:

Do you add the Epsom salt directly to the grow bed?