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An Overflow to the Sump

FAQ - Read the frequently asked questions about "Overflow To External Filter".

There are many ways to filter the aquarium water and one of them is to drain water out of the tank to the sump. These filters (sumps) unilke of the canister ones are not closed therefore water needs to be taken from the aquarium to ensure the water cycle: aquarium – filter – aquarium. In canister filters, there is a pump placed in the filter. After the filter starts, the vacuum will occur, water is sucking to the filter actively and during the power or pump failure water did not flow from the canister filter because it is sealed. In case of the open filters or sumps you want to drain the water from the aquarium through the overflow. One of the options is to use a small overfow box but in this plan we will be dealing with the overflow through the hole in the tank wall. The hole may be drilled in the bottom, back or side wall.

I have drilled the hole 45 mm in diameter in the back aquarium wall. The reasons why in the back wall:
1. The pipe leaving the aquarium is hiden behind it.
2. Easier handling with the bulkhead than that in the back wall. The hole in the bottom needs to drill the hole also in the base board under the tank and also fixing the bulkhead while lying under the tank is much difficult. Beside this, if the bulkhead is fixed permanently, aquarium cannot be moved from the stand and placed directly on the bottom side as there is a lurking bulkhead. When we would try to put this tank back to the stand, mainly the bigger tank which weighs a few tenths of kilograms, there could be a problem to fit the bulkhead to the hole in the base board accurately. It is possible, sure, but I have avoided the needless problems.
3. In case of the bulkhead tightness damage, it is easier to control and repair the bulkhead or pipe failure as the pipes are behind the tank. There must be some distance between the tank and the wall, sure.

Obr. 1  - Schéma prepadového potrubia Let’s continue with the overflow alone. All the system is shown in Pic. 1. In the back wall of the aquarium, there is the drilled hole 45 mm in diameter and centered 15 cm from the left wall and 15 cm from the bottom. The hole is reinforced by the drilled (45 mm hole) glass plate (10 mm thick) measuring 30 by 30 cm. The centre of the hole in this glass plate fits with the centre of the hole in the aquarium. Into the hole has been inserted the bulkhead. Formerly, I sealed the bulkhead with the silicone gasket. After the first water filling the gasket started to leak so I had to drain and dry up the tank, and to stick the bulkhead for ever. I sealed the bulkhead with a new silicone gasket again but I have added also the silicone glue around the whole bulkhead from the outer and inner side. After the silicone has dried, the tank was filled with water and everything was right. Pic. 2 shows the connection of the bulkhead with the other parts out of the aquarium. Pic. 3 shows the side view at the complete overflow in the tank. Inside of the tank, there is an elbow connected to the pipe heading up. Pic. 4 and Pic. 5 show the seal of the bulkhead by the silicone glue from the outer side of the tank. Another elbow is connected to the pipe heading to the water level from the bulkhead (Pic. 6).

Pic. 2 – Construction of the bulkhead and other outer parts Pic. 3 – Connection of the bulkhead and pipes Pic. 4 – Outer view at the bulkhead Pic. 5 – The bulkhead from the outer side of the tank Pic. 6 – The general view at the part of the overflow in the tank

The overflow could now stay as it is but the flushing sound would be produced during the water flow through the elbow which is located at the water level. I solved this problem by adding another elbow. This elbow is heding down to the bottom. It causes the sound of water falling into the vertical pipe (grey) is muffled. I have drilled the holes 5 mm in diameter in the last elbow around. They serve for taking the air from the water flowing into the pipe (Pic. 7 and Pic. 8). Do tohto kolena som vsunul krátku trubku z PVC, do ktorej som tiež navŕtal otvory. Koniec PVC trubky, kadiaľ vteká voda z akvária, som prekryl tkaninou, aká sa používa na výrobu akvaristických sieťok na odlov rýb a zafixoval som ju prstencom odrezaným z polyetylénovej trubky rovnakého priemeru, ako je koleno (Pic. 9).

Pic. 7 – View at the pipe from above Pic. 8 – Sucking pipe in the tank with the deareation holes Pic. 9 – Net on the sucking opening

The net prevents entering the fishes into the pipe. Although the pipe is behind the background (Pic. 10, Pic. 11 and Pic. 12), near the bottom, there is a hole through which the fishes can pass easily. Outer part of the pipe is connected to the flexible hose (Pic. 13).

Pic. 10 – The overflow pipe behind the background Pic. 11 – Side view at the pipe behind the background Pic. 12 - Internal mechanical filter behind the background Pic. 13 – Pipe connection behind the tank

Pic. 14 and Pic. 15 show the hose which was used for draining the water to the filter. It fits for this purpose perfectly as it is light, flexible and has a right diameter. An 1 1/2" ball valve is connected to the end of this hose before it enters to the filter (Pic. 16 and Pic. 17). It serves to the flow control from aquarium to the filter. It is important part of the system as without it would be impossible to balance the water flowing from the tank and returning water from the filter.

Pic. 14 – Flexible hose draining the water from the aquarium Pic. 15 – Flexible hose – a detail Pic. 16 – Flow control valve Pic. 17 – A valve before the filter

Water is returned to the tank by Sicce IDRA pump (Pic. 18) with a maximum flow rate 1300L per hour. The pump is connected with the flexible washing machine sewage hose (Pic. 19). This hose is furnished with a 1/2" ball valve (Pic. 20). Anyway, it is fully open all the time and it can be omitted. It is rather needed to control the water flow from the aquarium than to screw the pump. I recommend to oversize the hole in the tank and the pipe draining the water to the filter because it makes some backup for using the more powerful pump or multiple pumps. I could use another pump with no problems because the valve controlling the flow to filter is partly closed and I can increase the amount of the water flowing from the tank. The hose leading from the filter passes through the open in the canopy and its end joins just at the tank water level (Pic. 21). The water flow takes the air and the water is aerated.

Pic. 18 - Sicce Idra return pump Pic. 19 – The hose connecting the pump and the tank Pic. 20 – The pump valve conrol Pic. 21 – The hose from the filter entering the tank


I have been asked many times if the filter will overflow when the power is off.or in case of the pump failure. The answer is: NOT AT ALL! To justify this statement I’m describing the overflow operation.

1. The initial status: Filter chambers are full except of the last one, where the pump is placed. This chamber is half filled.
2. The pump goes ON: Water in the tank rises. Once the water reaches the opening into the pipe in the tank (Pic. 8 and Pic. 9), water starts to drain form the tank to the filter through the bulkhead. Herein are important the holes in the drain elbow in the tank (Pic. 8) which allow to take an air away from the pipe and also eliminate the water flow noise. I have drilled many of these holes as it is impossible to count the number of them and it is simple to caulk few holes if needed. If water flows to quickly, you can caulk a few holes with some silicone sticks. Water flows through the filter chambers and the pump returns it back to the tank. An optimal water level was adjusted by the valve at the hose draining the water to the filter and by the holes at the elbow.
3. The power/pump goes OFF: Water level in the filter rises until the water level drops under the opening (elbow with the net) into the pipe in the tank. Filter should have some backup which is in my case 1/3 of the last chamber where the pump is placed. This 1/3 of the last chamber must stay empty also during the filter operation. It is filled with water during the power/pump failure.
4. The pump goes ON: Water accumulated in the filter returns back to the tank, the water level in the tank rises until it starts to spill into the elbow with the net and the cycle continues from point 2 described above.

TIP: In filter, there must be a few litre backup by the aquarium volume. In my case it takes about 15 L in 419 L aquarium. You should think about it during the planning the filter dimensions and mainly the individual main dividers hight.

FAQ - Read the frequently asked questions about "Overflow To External Filter".

DISCLAIMER: By building this DIY project you agree not to hold the author responsible for any injury or bodily harm you may cause to yourself or others. Read all safety instructions pertaining to equipment prior to use.

Copyright © 2003 - 2012 Robert Toman



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