The Planted Tank Forum banner
1 - 11 of 11 Posts

·
Registered
Joined
·
481 Posts
Discussion Starter · #1 ·
70w MH over a 24x20x20 tank. Am I asking for trouble?

The pendant will be mounted to allow for adjustment in height. I'm thinking with this deep of a tank and hanging the pendant high off the water, I should be ok w/o having to go high tech. The tank is a converted reef with an internal overflow so I don't want to go CO2 if I don't have to. Willing to do excel if need be. Thinking a mix of anubias, crypts and vals for height.

-Charlie
 

·
Registered
Joined
·
1,890 Posts
There are so many things to consider. You should be fine in the long run after you get the tank adjusted. At first you are probably going to have alot of algae. Once you get it set up and stable I would get some guys to keep the algae under control. Otos, Amanos, Nerite snails. I would also watch the amount of time you have the light on for the first couple of months. I will be in the same boat as soon as my glass pipes get in and I make a hanger for the 70 watt light that I have.
 

·
Premium Member
Joined
·
195 Posts
Hi, I had a 15gal tall tank (24inches high), non-CO2 with 120 Watts of MH (70W+50W) with a reflector kit-bashed from a standard hanging pendant fixture (see included pics). Once placed atop the tank, the lights were about 8inches from the water surface. The wattage and the distance was premeditated to give about 70 micromols/m2/sec of photosynthetic light at the bottom of the tank (which I found is a good amount of light for riccia and glosso etc.) The substrate, however, is a nutrient rich loamy yard soil and not standard planted aquarium substrate which usually are pretty lean when it comes to nutrients. For me, I prefer the continuous full spectrum of a high CRI metal halide bulb compared to the look of a spiky discontinuous spectrum of fluorescent light. With a high CRI (color rendition index), it looks like sunlight which really brings to life the color and feel of the tank.

MH light fixture built into canopy:
In this picture, the PAR meter reads 862 micromols/m2/sec of photosynthetic light when measured at the light.



Tank Using 120W MH:
This is the tank using the 120W of MH. At the bottom of the tank, the PAR values are around 70 micromols/m2/sec of light. This is about the threshold for growing riccia attached to stones, or for glosso to grow compact and horizontally.


Cheers!
 

·
Premium Member
Joined
·
195 Posts
Did you find you needed to supplement w/ CO2 at all? That's really the thing that is holding me back on this idea.
No, for this tank, I was inspired by the writings of Diana Walstad in her book "Ecology of the Planted Aquarium". In it, she tackles the science and philosophy of CO2 through "biology" instead of "technology". But that requires a very active approach to your substrate design, tank loading, and water change regime.

A moderately rich yard soil with a moderate amount of organic matter will supply CO2 sufficient for most aquatic plants (at least, that I have grown). However, the potency will run out over time and what you'll be left with is a tank substrate that is biologically "slower" and proportional in nutrients to the inputs into the tank (i.e. dead plant matter, fish waste, food waste, and water changes).

But I find that I rebuild my aquascapes and replenish the soil about every 12 months anyway, so this works for me.

Due to my moderate success with soils and MH lighting, this is where I diverge from the LowTech philosophies and understandings. The substrate is the "life-heart" of your planted aquarium. Too many people underestimate the value of a proper substrate, and hence it skews their perception of lighting, CO2, and algae.

In short, if you pair your MH light with a proper substrate and have minimal fish and inverts, you should do ok. The hard part, without measuring the photosynthetic active radiation (PAR) of the lights, is to know when to let algae run through it's "cycle", or if you are truly overdriving the biological speed of your substrate; i.e. it's ability to cycle nutrients and create CO2.

This is where the PAR meter, knowledge about your substrate, and actual tank experience come into play.

Unfortunately, the timeline of how your tank responds to environmental changes takes course over many weeks and months, not days - which is the observation span of most hobbyists. This is especially true in a non-CO2 tank where the biological dynamics are much slower than a tank artificially injected with CO2.

In the past, I have been asked whether I think ADA Aquasoil or Eco-Complete are good substrates. I've never used them, but even though they are soil-based, I question whether they are proper in terms of a soil's ability to host the bacterias that are necessary to cycle the nutrients that are inherent to the substrate in question. I also question whether these substrates have a full range of nutrients for the plants.

When I used my back yard soil, I sent it to a testing lab where they provided a break down of all the major nutrients and minerals, as well as checking for harmful chemicals and substances.

Unfortunately, there is no simple answer to your question because there are too many interactions that take place in a planted aquarium. All I can say, is that with some care, I have used MH over a non-CO2 tank with success.

Cheers!
 

·
Registered
Joined
·
75 Posts
Hi Jeremy,
Is there other ways of measuring the micromols/m2/sec of photosynthetic light without a PAR meter? I'm having 3 x 150W M.H for my 6ft long tank. The M.H bulbs(Osram Powerstar) are about 7 inch above my water level. Water level to base substrate is about 18 inches. I turn on the lights 2 x 4 hours daily. Is that too much?

K.C
 

·
Premium Member
Joined
·
195 Posts
Hi Jeremy,
Is there other ways of measuring the micromols/m2/sec of photosynthetic light without a PAR meter? I'm having 3 x 150W M.H for my 6ft long tank. The M.H bulbs(Osram Powerstar) are about 7 inch above my water level. Water level to base substrate is about 18 inches. I turn on the lights 2 x 4 hours daily. Is that too much?

K.C
Unfortunately, I don't think there's another way to measure PAR without a meter. Given your description, it sounds like you have one 150W MH light for each 2ft across the length of your tank. I'm trying to envision my pictured tank (earlier post, above) multiplied by three times horizontally. The biggest difference here is that I think we have different MH bulb/reflector types. And that's going to change the PAR values and light distribution in the tank. If I had to guess, I'd say you were in the range of 60-120 umol/m2/sec at the bottom of your tank - which is approaching moderate light (compared to "low" light, or "high" light). As mentioned in my previous response above, a good nutrient rich substrate with some organic matter content will be required if you are not supplementing with CO2. On the other hand, if you inject CO2+nutrients, then I would guess you're totally fine and in the ball-park of what I call "sufficient light for thriving aquatic plants".

But I'm not sure what you mean by running your lights 2x4 daily... You mean you turn on the lights for 4 hours, then turn them off (for some time), and then turn them on again for another 4 hours?

Whatever the case, it sounds like you are limiting the photo period, either because of your daily schedule, or some other reason. If you have a limited substrate and no CO2, then I wouldn't shorten the photo period, I would just raise the lights and run them 10-12 hours. Overall, I don't believe in shortening the photo period in planted aquariums. The plants that most of us grow are originally from the tropical latitudes which receive about 10-12 hours of light per day. I would say that making the photo period shorter in a non-CO2 tank only limits the amount of time the plants have to photosynthesize and produce the necessary elements needed for growth. In a non-CO2 tank, CO2 is created much more slowly by the biological processes in the tank. Having a longer photo period will give enough time for those processes to happen and the subsequent CO2 to be used by the plants.

I would say that a shorter photo period would be OK in a CO2 injected tank because the plant growth is so much more accelerated.


Cheers.
 

·
Registered
Joined
·
75 Posts
Thanks Jeremy,
I'm injection CO2 at the rate maybe 6-7 bps(not very sure,can't really count looking at the bubble counter). You are right that I on my lights for 4 hours and then off,giving the plants a rest period and later on again for another 4 hours. In fact, I don't mind having my lights on for maybe 10-12 hours daily but since I'm using M.H, there is always a fear of aglae bloom. So I set my CO2 / lightings on timer :
7am : CO2 injection start
8am : Lights on (all 3 bulbs)
11.30am : CO2 cut off
12pm : Lights off
7pm : CO2 start injecting
8pm : Lights on (all 3 bulbs)
11.30pm : CO2 cut off
12am : Lights off

I do dose potassium sulphate & calcium nitrate on a weekly basis after W.C at 40%. I also add liquid Iron + trace elements every other day.

Cheers,
K.C
 

·
Premium Member
Joined
·
195 Posts
I'm injection CO2 at the rate maybe 6-7 bps(not very sure,can't really count looking at the bubble counter). You are right that I on my lights for 4 hours and then off,giving the plants a rest period and later on again for another 4 hours. In fact, I don't mind having my lights on for maybe 10-12 hours daily but since I'm using M.H, there is always a fear of aglae bloom. So I set my CO2 / lightings on timer :
7am : CO2 injection start
8am : Lights on (all 3 bulbs)
11.30am : CO2 cut off
12pm : Lights off
7pm : CO2 start injecting
8pm : Lights on (all 3 bulbs)
11.30pm : CO2 cut off
12am : Lights off

I do dose potassium sulphate & calcium nitrate on a weekly basis after W.C at 40%. I also add liquid Iron + trace elements every other day.

I see, thanks for the clarification. I've heard of people implementing rest periods into their photo period. But I don't know enough about the physiology of aquatic plants to know how a shut-down/start-up in the middle of the day affects their biological processes.

At any rate, your are injecting CO2+nutrients so that shifts the balance quite a bit. I'm curious though: I'm guessing that you have some level of success with your lighting and photo period regime... So, what prompted your original question in regards to your MH lights? Is your main concern algae, or plant photosynthesis?

With my own tests (and others online here leading the way), I believe it has been shown that you can have PAR values well into 300-600 micromoles/m2/sec and not have algae if you are dosing sufficient CO2+nutrients. And, indeed, I'm sure that you have PAR values approaching 300+ umoles/m2/sec near the surface of your water column, at least directly under your MH lamps.

Originally, you asked if the combination of your MH's and photo-period were too much... And my best guess is that, no, it's not too much given that you dose CO2+nutrients. But if you are having problems with algae, and you don't want to change your lighting, then you need to really evaluate if your CO2 concentration is sufficient, and whether your nutrient dosing is sufficient.

I just went through a period with one of my tanks where I had underestimated the amount of nitrates that were needed in the tank. I was originally dosing 5ppm every other day.... But it turns out that what my tank needed was 15ppm of NO3 every other day to keep from running out. Once I observed that, the green dust algae that had appeared, slowly disappeared over the course of a few weeks.

The thing that I had underestimated was that, in the beginning, there was a much smaller plant mass growing in the tank, but when the plants grew into a thick mass over time, I wasn't originally sensitive to the fact that I needed to supply a lot more nutrients :) I thought my original estimate was "more than enough". Apparently, it wasn't.

Cheers!
 
1 - 11 of 11 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top