Backyard Aquaponics
A place to discuss aquaponics

I have a 55gl indoor fish tank w/ a grow bed on top. The plants leaves in the grow bed are starting to yellow. I assume its a magnesium deficiency and wanted to use Epsom salts. How much and how exactly do I apply it? and what effect will it have on my fish? Also, algae is starting to get thick in some areas of the grow bed... could that be the problem? is the algae is taking most of the nutrients from the plants?
(below may be useful information)
- I could be feeding the fish too much.
- im growing small plants like basil, lettuce, etc.
- The lights stay on all but 4 hours a day (20 hours on).
- siphon runes every hour for 15 minutes
- there's about a quarter inch of dry rock on top - (going to try to raise the plants and add more rock to increase the dry section to an inch)
- algae is not out of control in the tank (thou i do have a snail problem that im trying to decide between assassin snails or clown loaches to solve it with).
- Nitrate and ammonia stable
- Ph is around 7 (which spikes, probably because of the algae)

Any advice on the effect of epsom salts or other alternatives?

Hi dillweed,

Yellowing of leaves is often a result of iron deficiency from what I have read. If you do buy some iron be aware that there are 3 different types and that of those 3, 2 (EDDHA and DTPA) are most suitable for AP. DTPA is easier to acquire here in Australia than EDDHA and unlike some EDDHA, DTPA won't turn your water blood red (speaking from experience). The reason for the different Iron types is that they are soluble at different pH levels and EDDHA and DTPA have a wider range pH within which they are soluble.
Here is a link to an Iron deficiency topic
viewtopic.php?f=3&t=17117&start=135
hope that helps

Even small amounts of algae will rob huge amounts of Nitrates from your system. When cycling my IBC system the FT developed a dinner plate sized patch of algae in one spot where direct sunlight was hitting it. It took three days for the patch to develop from nothing to plate sized, over that 3 days the Nitrates in the system went from 40ppm to 0ppm... and there were no plants in the system. Also. if you are having daily pH fluctuations, then yes, it's probably the algae.

If your system pH is 7.0 and you are feeding a good quality commercial fish feed then I doubt very much you have an Iron deficiency, but some photo's would help us diagnose the problem.

I would recommend you have your GB's max flood level 40mm below the surface of the gravel, I've tried 25mm (1 inch) and was getting massive evaporation (I didn't leave it long enough to develop algae), I dropped it to 40mm (1.5 inch) and the evaporation problem dissipated immediately. I would also recommend you cover your FT so no direct light can contact it. Algae needs light and nutrients to grow, we don't want to remove the nutrients, so we have to stop the light.

I would also add Maxicrop occasionally, for your system about 15mm per week until the plants pick up, then 15ml per fortnight. The Maxicrop with Iron version is probably the best option.

Here are some pictures of my plants. I grabbed a few of the netpots and raised the plants a lil more above the water line. Not sure if its made a difference though.

What are your Nitrate readings? Yellowing without the intervenal chlorosis is sometimes a lack of nutrients. It can also be a more advanced Iron deficiency.

There are some plants that appear to have an iron deficiency (interveinal chlorosis is showing up) which is common early on (you can use Maxicrop plus iron at the pH your running, you don't need chelated iron). If the pH goes over 7.5 or so get some chelated iron using the suggestions that Tom gave. It was difficult to tell whether the new or the old leaves were affected first from the images. Should be the new leaves initially with iron.

There's some guesswork here but Covering the tank and providing iron should help get the plants looking better. The Maxicrop will add some other beneficial elements from seaweed. I would hold off on the Epsom Salts for now since I don't see any clear evidence of it being needed.

Hope this helps