# Glass top vs no top



## monty67 (Sep 22, 2010)

So i'm running a GLO T5 HO fixture on my tank and i've always just had it sit on top of the glass top about 1/4 inch raised for a little airflow. I was always instructed to keep a top just to keep in heat, lower evaporation, and to keep the fish from jumping out (course i still had a few excape through the hole near the filter). 

Trying to get back into the hobby (I've been pretty lax about it the last few years) and be a little more serious about setting up and maintaining the tank. Did some reading and found some info that said the glass top will block the uv light that the plants need. How accurate is that? Should i be removing the glass top? The only fish i have that might want to jump is a cory that we all know will shoot to the top for a quick hit of air or whatever they're doing.

If i have to remove the top and raise the fixture 4 inches or so above the water will it really make that much of a difference in the plant growth? Sorry, this is a planted aquarium.


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## Nue (Dec 27, 2009)

I wouldn't worry about loosing light from the glass top.


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## captain_bu (Oct 20, 2007)

Raising the light 4" is going to reduce the intensity more than using a glass top will.


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## Abrium (Jan 7, 2011)

I would like to continue the question/debate of glass top vs no glass top if I may? I am still yet a beginner but alas as I search the web I am unable to find many lighting research resources that can accurately describe what happens or what the difference is between using a glass top and not using a glass top. Is there light diffusion, amplification, or intensification at a level that is MASSIVELY prohibitive to the growth of plant life in a fresh water planted tank? I'm aware there are multiple variables to be dealt with so I'll go over what my setup is so that more experienced planted aquarists can provide me input in regards to the glass top. 

125 gallon tank
Lighting: 2 coralite 36” fixtures both are outfitted with 21 watt 6700K & 21 watt 10000K T5 bulbs
Substrate: 50/50 mix of flora max and large sand ~ 2mm to 5mm
That brings me back to the hood. I would like to know the impact of having the glass hood put in place while I attempt to grow different types of aquatic vegetation. I’m not starting at the top. I have recently, since upgrading the lighting, purchased a “prolific” and “unstoppable” grower to ensure success… My first plant is Java Moss. I have attached the moss to a rock but as I was standing back and admiring the set up I happen to notice the glass hood and how many water spots/drops there were and that is when I began to wonder about the hood vs no hood issue and what impact it may have on the lighting at the floor level of the tank.
I have attached some photos, can anyone provide me any advice or lean me towards a thumbs up or thumbs down? I know about wpg, lsi, and the ultimate measurement… PAR. However, I don’t have a way to measure PAR at the substrate level of my tank. 

I just want to ensure I’m on the right track.

Water on the under side of the hood









From under the water level looking up:









My Moss:


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## majstor76 (Jun 11, 2010)

On TheKrib therse text about measuring losses with glass top and they found out that dirty glass top loses about 5% light in contrast to no top. 
Well, i want that 5% . I had glass top long time ago and seeing all that calcium deposits and water , i removed it and never returned it.
You can try to photograph aquarium with or without top, camera should be able to see difference (if any).
Its interested that in the same measuring they found that surface rippling takes about 5-15% of light.


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## captain_bu (Oct 20, 2007)

Abrium said:


> Is there light diffusion, amplification, or intensification at a level that is MASSIVELY prohibitive to the growth of plant life in a fresh water planted tank?


If using a glass top was massively prohibitive to growth then everyone who uses a glass top would be finding it difficult to grow anything and that is simply not the case.

Researching the relationship between lighting levels, CO2 and fertilizers is going to yield more useable info for you than worrying about potential light loss from using a glass top.

FWIW.... it is helpful with a new tank to plant heavily from the start with fast growing stems. Putting T5 lighting over an empty tank is an invitation to algae problems. You don't have to use plants you plan on keeping long term, get something cheap and fast growing but get some plants in there. The bacteria on the plants will also help your tank to cycle quicker and help your filter establish the beneficial bacteria you need to process waste.


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## Sharkfood (May 2, 2010)

Plants don't need any appreciable amount of UV light as far as I know.

I don't put tops on my tanks, but I do have to top them off 2-3 times during the week due to evaporantion.


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## SleepyOwl (Sep 23, 2007)

I wipe my glass tops down whenever I do a water change. Every once in a while I take them to the sink to do a bit of scrubbing. Keeps them mostly clear, and it is worth it to me to lower evaporation, and safety of mind since my light fixture does not have a splash guard.


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## HypnoticAquatic (Feb 17, 2010)

you can lose about 30% of light all depends on how clean dirty the glass is, also why they make starphire glass. idk how u can compare rasing vs glass top without a par meter? yes u will lose more water with it off but its all choice clean glass more or top off?


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## captain_bu (Oct 20, 2007)

HypnoticAquatic said:


> you can lose about 30% of light


Curious...where did you get this figure from?


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## HypnoticAquatic (Feb 17, 2010)

this is a simple ? thats asked over and over even on here if u search you will see. this is why people want starphire glass cause it cuts out less but is more $. ive known about that it can cut about that much for a long time but i cant cite a specific place on where i remember having it, a little use of the internet will show u. even the windows in ur house do this. tpt search or google


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## scape (Nov 27, 2010)

I wouldn't worry to much about reduced light transfer with a t-5 ho, but it is up to you. I love the look of the open water. You do have to top off the tank and dust finds its way in all the time, but it looks great!


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## SleepyOwl (Sep 23, 2007)

Yes, an open top tank does look great. Not so much if you have cats and small children though.


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## scape (Nov 27, 2010)

^ good point he he :icon_smil


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## mmelnick (Mar 5, 2010)

Yes, glass will filter out UV light. But the glass in most light bulbs filters it out before it even leaves the bulb. There are some exceptions with certain types of metal halide lighting though. In those cases the light fixture has a glass shield to silter out the UV instead of the plexi shield that a lot of other fixtures have.

Even in reef tanks with highly demanding coral UV isn't required. Although it does have certain benefits.


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